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CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  /  Institut  Canadian  de  microreproductions  historiques 


T«chnical  and  Bibliographic  Notaa/Notas  tachniquaa  at  bibliographiquaa 


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copy  which  may  ba  bibliographieally  uniqua, 
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raproduction,  or  which  may  aigniflcantly  changa 
tha  uaual  mathod  of  filming,  ara  chackad  balow. 


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Coiourad  covart/ 
Couvartura  da  coulaur 

Covar»  damagad/ 
Couvartura  andommagte 

Covars  rastorad  and/or  laminatad/ 
Couvartura  raataurte  at/ou  palliculAa 

Covar  titia  misting/ 

La  titre  da  couvartura  manqua 

Coiourad  maps/ 

Cartes  g6ographiquas  an  coulaur 

Coiourad  inic  (i.e.  othar  than  blua  or  black)/ 
Encra  da  coulaur  (i.a.  autra  qua  blaua  ou  noira) 


I     I   Coiourad  platas  and/or  illustrations/ 


D 


Planchas  at/ou  illustrations  an  coulaur 

Bound  with  othar  material/ 
RailA  avec  d'aqtras  documanta 

Tight  binding  may  causa  shadows  or  distortion 
along  interior  margin/ 

La  re  liure  serrde  peut  causer  de  I'ombre  ou  de  la 
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Additional  comments:/ 
Commentaires  supplAmentaires; 


L'Institut  a  microfilm*  la  mailleur  exemplaire 
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modification  dans  la  mithoda  normale  de  f ilmage 
aont  indiquAs  ci-dassous. 


I     I   Coiourad  pages/ 


v/ 


n 


Pagea  da  coulaur 

Pages  damaged/ 
Pages  endommagAes 

Pages  restored  and/o( 

Pages  restaurias  at/ou  pellicuiies 

Pages  discoloured,  stained  or  foxe« 
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Pages  detached/ 
Pages  dAtach^es 


I — I  Pages  damaged/ 

I      I  Pages  restored  and/or  laminated/ 

r~7|  Pages  discoloured,  stained  or  foxed/ 

I     I  Pages  detached/ 


Showthrough/ 
Transparence 


I      I    Quality  of  print  varies/ 


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Includes  supplementary  material/ 
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Only  edition  available/ 
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Les  pages  totalement  ou  partiellement 
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This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  film*  au  taux  de  rMuction  indiquA  ci-dessous. 


10X 

14X 

18X 

22X 

26X 

30X 

J 

12X 


16X 


2DX 


24X 


28X 


32X 


Th«  copy  fiim«d  here  has  been  reproduced  thanke 
to  the  generosity  off: 

National  Library  off  Canada 


L'exemplaire  ffilm*  ffut  reproduit  grice  A  la 
gAnArosit*  da: 

BibliothAque  nationale  du  Canada 


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or  illustrated  impression. 


The  last  recorded  fframe  on  each  microffiche 
shall  contain  the  symbol  —»■(  meaning  "CON- 
TINUED"), or  the  symbol  y  (meaninfi  "END"), 
whichever  applies. 


Lee  imeges  suivantes  ont  At*  reproduites  avec  le 
plus  grand  soin,  compte  tenu  de  la  condition  at 
de  le  nettetA  de  l'exemplaire  ffilmA,  et  en 
confformitA  evec  les  conditions  d^i  contrat  de 
ffilmege. 

Les  exemplaires  originaux  dont  la  couverture  en 
papier  est  ImprimAe  son^  ffilmAs  en  commenpant 
par  le  premier  plat  et  en  werminant  soit  par  la 
derniAre  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration.  soit  par  le  second 
plat,  seion  le  cas.  Tous  les  autres  exemplaires 
originaux  sont  ffilmAs  en  commenpant  par  la 
premiAre  page  qui  comporte  une  empreinte 
d'impression  ou  d'illustration  et  en  terminant  par 
la  derniAre  page  qui  comporte  une  telle 
empreinte. 

Un  des  symboles  suivants  apparaftra  sur  la 
derniAre  image  de  cheque  microffiche,  selon  le 
cas:  le  symbols  -^  signiffie  "A  SUIVRE",  le 
symbols  ▼  signiffie  "FIN". 


Maps,  plates,  charts,  etc.,  may  be  ffilmed  at 
difffferent  reduction  ratios.  Those  too  large  to  be 
entirely  included  in  one  exposure  are  ffilmed 
beginning  in  the  upper  lefft  hand  corner,  lefft  to 
right  and  top  to  bottom,  as  many  fframes  as 
required.  The  ffollowing  diagrams  illustrate  the 
method: 


Les  cartes,  planches,  tableaux,  etc.,  peuvent  Atre 
ffilmAs  A  des  taux  de  rAduction  diffffArents. 
Lorsque  le  document  est  trop  grand  pour  Atre 
reproduit  en  un  seul  clichA,  11  est  ffilmA  A  partir 
de  I'angle  supArieur  gauche,  de  gauche  A  droite, 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'images  nAcessaire.  Les  diagrammes  suivanta 
illustrent  la  mAthode. 


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FOR 


OLD  AND  SILVE 


IN  NORTH  AMERICA. 


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ARTHUR  LAKES. 


:4»5isTAirr  Editor  "  The  Colliery  Engineer  and  Mbtal 

Late  Professor  op  Geology  at  the  State  School 
OP  Mines,  Gk>LDEN  City,  Colorado. 

•I      Au/kor  of  ^*  Geology  of  Colorado  and  Western  Ore 
tVtir  Deposits*  *' Geology  of  Colorado  Coal 


Deposits,''  Etc. 

^^^H^f~ 

^^^^Mp»'.'' 

SECOND   EDITION. 

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SCRANTON,  PA. 

'^ 

THE  COLLIERY  ENGINEER  CO. 

1896. 

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261219 


Entered  according  to  the  Act  of  Congress  in  the  Year  1896 

By  Thk  CoLLiEKV  Encinekk  Co., 
Id  the  Office  of  the  Librarian  of  Congress,  at  Washingtoa. 


! 


I 


PREFACE  TO  FIRST  EDITION. 


In  preparing  thi^  little  work  the  author  has  felt  the  diffi- 
culty  which  arises  in  a  theoretical  dissertation  on  so  emi- 
nently practical  a  subject  as  prospecting.  It  seems  like 
giving  rules  and  prescriptions  for  hunting  or  fishing  or  any 
other  natural  or  practical  pursuit.  Though  theory  and 
practice  are  not  at  variance  when  happily  combined,  yet 
either  without  the  other  proves  very  unsatisfactory.  Thus, 
the  reader  of  this  book,  should  he  start  out  armed  only 
with  its  theory,  will  find  himself  for  some  time  pretty 
much  "  at  sea"  when  he  comes  to  actual  practice  in  the  field. 
As.  however,  he  gradually  obtains  some  piactical  experi- 
ence, he  may  find  this  little  work  of  use  to  him.  So,  also, 
the  seasoned  prospector,  who  has  hitherto  trusted  to  luck, 
keenness  of  observation,  intuition,  and  experience,  may  find 
himself  in  the  future  much  better  equipped  by  acquiring  a 
little  of  the  theory. 

Whilst  we  have  endeavored  to  give  the  prospector  all 
assistance  in  our  power,  as  to  the  best  means  of  educating 
himself,  describing  his  outfit,  etc.,  we  have  devoted  special 
attention  to  the  description  of  such  geological  and  other 
phenomena  as  he  is  likely  to  meet  with  in  connection  with 
his  work,  so  that  he  may  have  an  intelligent  idea  of  them 
when  he  encounters  them. 

We  have  selected  just  as  much  material  as  we  think  would 
be  most  interesting  and  useful  to  him,  saving  him  the  time 
and  trouble  of  wading  through  heavy  tomes  and  laboriously 
picking  out  from  a  vast  amount  of,  for  his  purpose,  super- 
fluous matter  that  which  he  will  most  require. 

The  work  is  intended  to  be  a  popular  one,  addressed  to 
the  average  student,  prospector,  and  miner,  and  to  the 
general  public. 

ARTHUR  LAKES. 

January  i,  1895. 


m^^^^m^i^^^mii^mmmmmmmmm 


■P»"i»iP^w^wwwwwwPi»»"»—w 


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PREFACE  TO  SECOND  EDITION. 


y 


The  kind  reception  given  to  "  Prospecting  for  Gold  and 
Silver"  by  the  mining  and  prospecting  fraternity,  as  well 
as  the  general  public,  has  made  necessary  a  second  edi- 
tion. In  this  we  have  added  to  the  text  sketches  of  some 
of  the  principal  prospecting  regions  of  North  America, 
which,  besides  illustrating  the  principles  presented  in  the 
work,  will,  with  their  maps  and  illustrations,  prove  useful 
guides  to  prospectors  who  may  venture  into  those  districts. 
Having  extended  the  scope  of  the  work,  we  have  accord- 
ingly g^ven  it  a  more  general  title,  namely :  "  Prospecting 
for  Gold  and  Silver  in  North  America." 

Respectfully, 

ARTHUR  LAKES. 

Boston  Building,  Denver.  Col.. 
October  i,  i8g6. 


CONTENTS. 


CHAPTER  PAOB 

I.— On    Prospecting— Preparation  and    Outfit   for 

Work,  7 

II.— The  Prospector's  Geology 25 

III.— The   Prospector's   Paleontology   or   Study    op 

Fossils 39 

IV. — The  Prospector's  Lithology  or  Study  of  Rocks,     50 

V. — The  Prospector's  Mineralogy 63 

VI. — Ore  Deposits 7a 

VII. — Various  Forms  of  Ore  Deposits.  .        •       .    88 

VIII. — Relation  of  Veins  to  Eruptive  Forces,        .        .    99 

IX. — Gold  Placers, iii 

X.— "Deep  Leads," 119 

XI. — Mining   Regions,  Showing  Examples  of  Ore  De- 
posits  125 

XII. — Ore  Deposits  in  Sedimentary  Rocks,     .        .        .162 
XIII. — Examining  and  Sampling  Mining  Properties,  Pros- 
pects or  Mines. 1&7 

XIV. — Prospecting  in  Various  Regions 198 

XV. — Geology  and  Mineralogy  of  Alaska,     .       .        .  210 

XVI. — British  America 213 

XVII.— California, 223 

XVIII. — Montana.  Dakotah.  Arizona,  and   New  Mexico,  232 
XIX. — The  Gold  of  the  Ortiz  Mountains  and  Gams- 

teo  and  Rio  Grande  Placers.  N.  M.,  .  249 

XX. — The  Gold  and  Silver  Ore  Deposits  of  the  Mbr- 

CUR  District,  Utah 255 

XXI. — Salting  Mines, 264 

XXII. — Prospector's  Tools,   and  How  to  Sharpen  and 

Temper  Them, 272 

XXIII. — Some  Elements  of  Mining  Law  Relating  to  Pros- 
pecting        .        .  280 


PROSPECTING  FOR  COLD  AND  SILVER 

IN  NORTH  AMERICA. 


CHAPTER  I. 

ON  PROSPECTING— PREPARATION  AND  OUTFIT  FOR 

WORK. 

The  regular  prospector,  as  a  rule,  has  at  some  time  of 
his  chequered  career  had  some  actual  experience  in  the 
mines  themselves,  from  which  he  has  learned  by  obtervap 
tion  the  appearance  of  different  ores,  their  different 
values,  how  the  veins  api)ear  on  the  surface,  how  to  open  a 
vein,  and  the  uses  of  pick,  shovel,  and  blasting  powder. 
In  a  word  he  is  a  miner  who  has  become  too  restless  to 
stick  to  steady  work,  and  so  follows  the  more  uncertain  and 
precarious  livelihood  of  seeking  for  new  and  undiscovered 
veins,  many  of  which  even  in  an  old  mining  district  may 
yet  be  discovered  covered  up  by  brush  or  debris,  whilst  a 
new  district  offers  a  most  enticing  field.  These  mineral 
veins  or  ledges  may  make  him  in  a  moment  a  compara- 
tively rich  man,  and  if  he  finds  them,  they  will  cost  him 
nothmg,  only  a  simple  compliance  with  the  inexpensive 
regulations  of  the  law.  So  the  life  of  a  prospector  offers 
many  attractions  to  one  who  is  restless  and  loves  to  roam 
and  loves  to  find  something  new  and  is  nof  afraid  of  consider- 
able hardship.  To  save  a  vast  amount  of  time  and  labor,  he 
should  acquire  knowledge.  Thus,  for  instance,  if  he  were 
prospecting  for  coal  he  would  be  wasting  his  time  in  hunt- 
mg  for  it  in  granite,  or  if  he  wf  s  hunting  for  the  precious 
metals,  he  would  lose  time  in  looking  for  them  among  the 


tanaltered  sedimentary  strata  of  the  prairie.  This  is  merely 
for  example,  but  an  infinite  variety  of  knowledge  is  neces- 
sary for  him  in  his  vocation,  besides  even  that  of  the 
simpler  elements  of  geology,  such  as  the  knowledge  of 
different  kinds  of  minerals,  and  their  value,  the  kind  of 
places  and  peculiar  rocks  they  are  associated  with,  their 
appearance  on  the  surface,  etc.,  etc.,  together  with  some 
knowledge  of  assaying  or  blowpiping  or  panning. 

In  i  newly  discovered  camp,  men  will  rush  In  for  a  few 
weeks,  work  a  little  in  the  different  mines,  sufficient  to  give 
them  an  idea  of  the  kind  of  ores  and  rocks  and  other  cir- 
cumstances in  the  locality,  and  then  will  strike  out  on  their 
own  account  aid  prospect  around  the  camp  for  new  veins 
or  extensions  of  those  already  discovered.  An  extension, 
by  the  way,  of  a  very  rich  discovered  lode  is  not  always  to 
be  relied  on.  Nature  seems  often  to  concentrate  her  riches 
at  one  point,  and  leave  the  extension  barren,  as  in  the  case 
of  the  Comstock  of  Nevada.  But  little  wealth  has  been 
found  outside  of  the  great  lode  and  mine  itself. 

The  best  education  is  in  the  mines  themselves,  so  a 
novice  on  arriving  at  a  mining  region  had  better  spend  as 
much  time  as  possible  in  practical  work,  in.  and  around  the 
various  mines,  before  he  launches  out  prospecting.  A 
prospector  can  rarely  carry  about  much  assaying  or  other 
apparatus  with  him  for  determining  the  character  or  value 
of  ores  he  may  find,  and  hence  it  is  well  for  him  to  accus- 
tom himself  to  these  ores  in  the  mines  themselves.  Also 
he  should  acquaint  himself  with  the  peculiar  ores  of  each 
particular  district,  before  he  attempts  to  prospect  in  its 
vicinity,  for  an  ore  such  as  coarse-grained  galena  in  one 
district  may  be  generally  rich,  whilst  in  another  it  is 
remarkably  poor  in  silver. 

The  best  previous  education  for  a  prospector  would  be  a 
course  at  a  school  of  mines,  where  ne  will  learn  the  ele- 
ments of  geology,  mineralogy,  assaying,  etc.,  and  next  to 
that,  practical  work  in  the  mines  themselves,  and  lastly  the 
prospecting  field.  A  little  knowledge  of  blowpiping  may 
also  help  him,  which  he  may  acquire  at  his  school. 

Having  left  his  school,  he  should  learn  the  practical 
use  of  the  pick,  drill,  and  blasting  powder.  By  working 
around  l,  Concentrator  he  will  learn  the  difference  between 
ore  and  gangue  rock ;  and  "  picking"  or  "  sorting"  ores  will 


teach  him  at  sight  the  values  of  ores.  The  prospector 
should  know  how  to  open  his  vein  or  ledge,  when  he  finds 
it,  with  pick,  shovel,  and  blasting  apparatus.  A  little  car- 
pentry will  teach  him  how  to  make  a  handwinch,  and  a 
fev;  lessons  in  blacksmithing  will  teach  him  how  to 
sharpen  and  temper  his  tools,  for  there  will  probably  be 
no  blacksmith's  shop,  or  carpenter's  either,  within  miles  of 
where  he  may  go.  Other  prospectors  will  teach  him  how 
to  use  his  pun  or  iron  spoon  for  testing  ores,  and  various 
other  dodges  and  makeshifts.  An  important  point  is  to 
learn  how  to  average  approximately  the  quantity  of  ore  in, 
and  value  of,  a  ledge  when  he  has  found  one.  Valuable 
ore  on  a  ledge  lies  in  pockets,  strings,  btmches,  irregularly 
distributed  through  the  quartz  or  other  material  of  the 
vein ;  he  should  learn  to  tell  at  sight  the  relative  proportion 
of  ore  and  gangue.  He  would  do  well  to  study  the  result 
of  working  ores  in  a  mill  or  furnace,  such  as  trying  to  esti- 
mate the  yield  of  bullion  of  the  ores  which  are  mined,  tak- 
ing them  m  weekly  or  monthly  lots.  With  some  such  pre- 
liminary knowledge  he  is  ready  for  the  field. 


HIS  OUTFIT. 

The  following  list  of  necessaries  by  Mr.  A.  Balch  in  his 
"  Treatise  on  Mining"  is  as  full  as  can  be  given  by  any  one, 
and  is  more  than  the  average  prospector  generally  needs. 

"  First.  Two  pairs  of  heavy  blankets  weighing  about  8 
pounds  each. 

"  Second.     A  buffalo  robe  or  a  blanket-lined  poncho. 

"  TAirJ.  Su.t  of  strong  gray  woolen  clothes,  pair  of  brown 
jean  trousers,  a  change  of  woolen  underclothing,  woolen 
socks,  pair  of  heavy  boots,  soft  felt  hat,  three  or  four  large 
colored  handkerchiefs,  a  pair  of  buckskin  gauntlets,  toilet 
articles,  etc.     All  should  go  into  a  strong  canvas  bag. 

*'  Fourth.  A  breech-loading  rifle  or  shot-gun  and  a 
revolver.  Around  his  waist  a  strong  sash  to  jarry  his 
holster  and  knife,  in  a  sheath.  His  ammunition,  if  his 
revolver  is  large  bore,  may  conveniently  fit  both  his  rifle 
and  revolver.     Pipe  and  tobacco. 

"Fifth.  A  sure-footed  native  or  mountain  pony.  A 
Mexican  saddle  with  its  saddle-horn,  straps,  etc.,  to  tie  on 
various  things,  such  as  his  pack,  bags,  water-canteen,  etc. 


/ 


10 

The  left  stirrup  may  be  fitted  with  a  leather  tube,  in  which 
the  rifle-barrel  may  be  placed.  A  strap  around  the  saddle 
horn  will  secure  the  gun-stock.  The  long  lariat  or  stake 
rope  for  tethering  his  horse  should  be  coiled  up  and  tied  by 
a  strap  to  the  saddle-horn. 

"  Stxth.  For  prospecting,  a  'poll'  pick  and  prospecting- 
pan  made  of  iron  or  a  horn  spoon  should  be  carried.  The 
pan  is  also  useful  besides  for  washing  out  sand,  as  a  dish 
or  bathing-vessel.  A  large  iron  spoon  for  melting  certain 
metals  is  likewise  to  be  carried,  and  in  some  cases  a  small 
portable  Battersea  assaying  furnace. 


A    PROSPECTOR   AND    HIS   OUTFIT. 


"  Seiienth,  A  frying-pan  8  inches  diameter,  of  wrought 
iron,  a  coffee  pot,  tin  cup,  spoon  and  fork,  and  matches 
in  tin  box,  pocket  compass,  a  spy-glass,  or  pair  of  field- 
glasses. 

''Eighth.  Provisions,  bacon,  flour,  beans,  coffee  or  tea, 
pepper,  salt,  and  box  of  yeast-powder,  all  packed  in  strong 
bags,  to  go  into  a  canvas  sack.  A  few  lessons  in  the 
kitchen  on  cooking  will  be  advantageous  before  starting. 


It 

"  Ninth.  Packing  the  bronco.  Place  a  folded  blanket  on 
the  horse's  back ;  on  this  lay  the  saddle.  The  saddle-bags 
contain  small  things.  The  bags  with  provisions  are  placed 
behind  the  cantle  of  the  saddle ;  on  top  of  this  the  bag  of 
clothing.  The  pick  goes  on  top  tied  by  a  thong.  Coffee- 
pot and  frying-pan  are  lashed  on  the  bags." 


A    PROSPECTOR  S   TOOLS. 


I,  2.  Picks. 

3.  Lone  handled  Shovel. 
4,  5.  Drills. 

6.  Heavy  Hammer. 

7.  Blasting  Powder. 


8.  Pan. 

9.  Horn  Spoon. 

10.  Iron  Spoon. 

11.  Fuse. 


Sometimes  a  prospector  takes  a  horse  to  ride  on  and 
another  as  a  pack  animal,  or  a  donkey  only.  For  grass  and 
water  for  his  horse  he  must  trust  to  the  country.  He  will 
fix  his  temporary  camp  in  some  suitable  location,  where 
these  are  to  be  found,  and  thence,  as  from  headquarters, 
prospect  daily  the  adjacent  country,  returning  nightly,  it 
may  be,  to  his  camp. 


BRIEF   SKETCH   OF   PROSPECTING. 

We  may  divide  the  ;:rospecting  for  the  precious  metals 
into  two  general  classes :  hunting  for  gold  in  gold  placers ; 
hunting  for  gold  and  silver  bearing  ledges  or  veins  or 
deposits. 

"  Placers"  are  places  where  gold,  having  been  torn  from 


fi 


the  ledges  and  rocks  by  denudation,  by  water  and  ice,  is 
swept  down  by  these  agencies  till  it  finally  finds  a  resting- 
place.     Gold,  being  heavier  than  quartz  or  country  rock. 


PANNING  GOLD  AT  CRIPPLE  CREEK,  COLORADO. 

sinks  to  the  bottom  first.  If  the  stream  is  violent,  it  will 
carry  the  gold  on,  if  fine,  till  it  comes  to  an  eddy  or  pool, 
where  the  waters  are  more  quiet,  and  there  it  will  sink. 
The  water  carries  the  clay  and  lighter  stones  still  further 


13 

on.  In  this  way  millions  of  tons  of  rocks  containing  more 
or  less  gold  disseminated  through  them  may  have  been 
reduced  and  the  gold  set  free,  or  the  gold  may  have  been 
derived  from  a  few  individual  gold-bearing  ledges  or  veins. 
The  prospector  takes  his  pick,  shovel  and  pan,  and  his 
horn  spoon,  and  finds  perhaps  an  old  dry  river-bed  where 
the  water  has  ages  ago  receded.  At  some  point  the  sides 
of  this  old  river-course  widen  out  suddenly,  forming  a 
basin.     "  Here,"  says  the  prospector,  "  there  must  have  been 


FINDING  THE   FLOAT. 


an  eddy,"  and  he  prospects  it  accordingly;  at  another  point 
he  finds  a  place  where  the  water  must  have  run  over  a 
rock  and  made  a  waterfall ;  at  the  bottom  he  digs  again. 

He  loosens  the  soil  with  his  pick,  and  shovels  it  out ;  at  a 
certain  depth,  which  may  be  from  5  to  20  feet  or  more, 
he  strikes  "bed-rock,"  which  may  be  granite,  shale,  sand- 
stone, or  some  other  rock.  Here  he  looks  for  nuggets,  and 
with  his  knife  digs  into  all  the  little  crevices  of  the  rock 
to  hunt  for  them  and  for  scales  and  wires  of  gold. 

Also  whilst  sinking  his  shaft,  he  pans  the  gravel  care- 
fully at  various  depths,  especially  where  there  are  streaks 


M 


of  clay  or  "black  sand."  The  latter  are  grains  or  little 
pebbles  of  magnetic  iron-ore,  a  common  accompaniment  of 
gold,  altered  relics  of  the  iron  pyrites  in  which  the  gold 
was  originally  contained. 

He  fills  his  pan  half  full  of  water,  throws  into  it  a  shovel- 
ful  of  dirt,  first  picking  out  the  pebbles,  stirs  the  mass  with 
his  fingers  till  the  water  is  fully  charged  with  the  clay,  and 
gradually  winnows  out  all  the  clay.  Filling  the  pan  again 
with  water,  he  gives  it  a  peculiar  circular  motion  and  each 
little  wave  of  sand  passes  off  till  the  whole  is  winnowed  off, 
and  at  last  he  sees  specks  of  gold  shining  free  in  the  bottom 
of  the  pan.  Then  it  is  not  difficult  to  estimate  approxi- 
mately the  amount  of  gold  to  the  bushel  or  cubic  foot  of 
earth  of  the  placer,  and  thus  to  estimate  the  approximate 
value  of  the  placer.  He  then  locates  or  stakes  out  his 
placer  claim  according  to  the  regulations  of  the  U.  S. 
Government,  which  by  a  single  individual  cannot  exceed 
twenty  acres. 

The  second  class  of  prospectors  are  those  who  try  to  dis- 
cover ore  deposits,  ledges,  or  veins,  "in  place,"  that  is,  in 
the  hard  rocks  of  the  hills. 

The  prospector's  first  effort  is  to  find  "  float."  A  vein 
outcropping  on  the  surface  becomes  oxidized  and  crumbles 
by  action  of  the  atmosphere,  rain,  etc. ;  pieces  break  off 
and  fall  down-hill.  Smie  of  this  float  is  barren  quartz  or 
country  rock,  others  may  be  mineralized.  Commonly 
"  float"  is  a  rusty,  spongy  mass  of  rock,  showing  besides 
iron  often  some  copper  stains,  and  in  it  there  may  be  grains 
of  galena,  pyrite,  or  some  other  ore.  He  tries  to  trace  this 
"  float"  to  its  home  in  the  ledge  whence  it  came.  Of  one 
thing  he  is  certain,  the  "  float"  must  have  rolled  douni  and 
not  ///  hill.  If  the  "  float"  is  fairly  scattered  over  the  lower 
zone  of  the  hill,  and  no  "  float"  is  found  above  that  zone,  on 
the  top  of  that  zone  he  will  hunt  for  his  ledge.  If  the 
"  float"  is  all  over  the  hill  he  assumes  the  ledge  is  on  the 
top. 

If  he  finds  his  "  float"  at  the  mouth  of  a  canyon  or  water- 
course, he  walks  up  that  water-course,  noticing  not  only 
the  "  float,"  and  its  diminishing  or  increase,  but  also  any 
peculiar  rocky  pebbles,  such  as  a  peculiar  porphyry,  per- 
haps, which  he  may  by  chance  recognize  again  further  up 
in  place,  and  give  him  a  hint  ias  to  whence  the  stream 


^i 


»5 

derived  most  of  its  material  of  pebbles.  He  notices  if  the 
"  float"  fragments  increase  as  he  proceeds,  and  whether 
they  suddenly  cease  at  a  certain  point:  at  that  point  he 
hunts  for  the  ledge  on  either  side  of  the  canyon,  and  breaks 
off  any  pieces  that  may  look  likely. 

Having  found  the  ledge  and  traced  its  croppings,  he  tries 
to  find  out  its  approximate  value.  This  he  does  by  break- 
ing off  at  intervals  along  it  likely  looking  fragments  of  the 
rock,  grinding  them  up  to  about  the  size  of  peas.  He 
mixes  these  well,  and  takes  a  half  of  them,  reducing  this  to 
fine  powder  and  again  halving  it,  till  of  the  whole  ledge 
he  can  carry  away  an  averaged  sample  of  a  few  ounces. 
He  may  wash  this  in  his  pan  to  see  if  there  is  any  free  gold 
in  it ;  other  ores  he  will  recognize  at  sight.  These  samples 
he  will  have  assayed  and  the  returns  will  show  the  approx- 
imate value.  He  measures  the  length  and  thickness  of  the 
vein,  and  examines  the  wall  enclosing  it. 

He  then  proceeds  to  locate  or  stake  it  out  by  measuring 
off  a  parallelogram  1,500  by  600  feet.  At  the  comers  of 
this  he  places  piles  of  stones,  and  in  one  or  more  of  them 
places  a  stake  of  wood  on  which  he  writes  his  name,  a 
description  of  his  claim,  and  the  date.  At  the  nearest 
recorder's  office  he  files  a  copy  of  this  document.  He  must 
do  a  certain  amount  of  improvement  work  on  this  annually, 
such  as  digging  a  ten- foot  hole  or  putting  up  a  cabin  or 
some  work  equivalent  to  the  value  of  $100,  so  as  to  hold  it. 
He  may  also  claim  a  mill-site  on  non-mineral  land  adjacent 
not  exceeding  five  acres.  Now  the  property  is  his  to  do  as 
he  likes  with  it. 


THE   GEOLOGICAL   TRAINMNG   OF   A    PROSPECTOR. 

One  of  the  first  things  for  a  prospector  for  gold  and  silver 
to  acquaint  himself  with  is  the  elements  of  geology.  He 
can  read  this  up  theoretically  in  many  excellent  treatises 
and  manuals,  such  as  LeConte,  Dana,  and  Shaler's  Manuals, 
and  Geikie's  Hand-Book  of  Field  Geology,  etc.,  and  become 
learned  in  the  names  of  eras  and  epochs,  and  the  jargon  of 
scientific  names  of  fossils  and  minerals,  and  varieties  of 
rocks ;  but  let  him  not  imagine  at  the  end  of  this  process 
that  he  "  knows  geology."' 

Geology  can  no  more  be  learned  by  means  of  a  book, 


i6 


without  field-work  and  the  actual  personal  contact  with 
nature  and  rocks,  than  chemistry  or  assaying^  can  be 
acquired  without  ever  using  a  test-tube  or  a  cupel.  Tue 
student  may,  perhaps,  be  unfavorably  situatea  for  this 
practical  field-work.  There  may  be  no  mountains  or 
upheavals  of  strata,  or  deep  natural  ravines  within  avail- 
able distance  to  study.  He  is  located,  perhaps,  on  the 
great,  monotonous,  flat  prairie.  Very  well,  then,  let  him 
study  what  lies  nearest  him.  This  same  flat,  monotonous 
prairie  has  an  interesting  and  wonderful  history.  Let  him 
read  up  what  he  can  find  about  this  in  his  books,  then  go 
out  and  examine  what  he  can  of  the  few  feet  of  horizontal 
strata  exposed  in  some  shallow  water-course  or  dry  ravine ; 
examine  minutely,  both  with  eyes  and  microscope,  the 
minerals  composing  these  strata.  Let  him  classify  and 
collect  and  note  the  different  kinds  of  pebbles  scattered 
over  the  surface,  or  in  the  bed  of  a  brook.  Let  him  specu- 
late as  to  the  cause  of  the  undulations  of  the  surface,  the 
deposition  and  peculiar  character  of  the  clays  forming  the 
soil.  Let  him  study  thoroughly  the  geology  of  his  native 
village,  his  immediate  surroundings,  first.  The  knowledge 
and  practical  habit  of  observation  so  acquired  will  lead 
later  to  more  extensive  studies  in  wider  fields.  A  student 
may  be  shut  up  in  a  big  city ;  let  him  study  the  paving- 
stones  of  the  streets  and  visit  the  stone-yards  of  the  masons. 
It  will  pay  him  better  to  take  a  trip  to  some  distant  moun- 
tain region  than  to  buy  another  expensive  book  on  geology 
after  he  has  mastered  the  first  bare  elements.  Nothing  like 
field-work,  eye  practice,  and  hammer  practice.  The 
student  should  endeavor,  whenever  he  possibly  can,  to 
verify  by  actual  vision  and  personal  expeiience  whatever 
he  reads  in  his  books.  When  traveling,  let  him  always 
carry  a  geological  hammer  with  him,  and  at  any  station  the 
train  may  stop  for  a  few  moments  step  out  and  try  to  get  a 
specimen  of  the  country  rock;  at  the  same  time  let  him 
study  all  he  can  of  the  geology  of  the  country  he  is  passing 
through  from  the  windows  of  the  train,  aided  perhaps  by  a 
geological  map.  The  genuine  prospector  is  always  looking 
about  him,  is  everlastingly  cracking  stones,  has  always  his 
eye  wide  open  for  "  something  kind  o*  curious." 

If  he  is  near  some  mountain  region,  where,  as  in  Colo- 
rado, the  whole  strata  of  the  earth's  crust  is  upheaved  and 


«7 


Cmctaocous 

t  o 

o 

OnKorn  Omoup  N 

Jun^aaio     J 


Tf^MSSIO 


III 
VI 


iCahboniferous 


H 


Silurian 
Cambrian   "^ 


Colo- 
Id  and 


Plate  I. 


A  Vertical  Section  of  the  Earth's  Crust  in  Colorado. 


i8 


/ 


exposed,  along  the  mountain  flanks,  in  the  depths  of  the 
canyons,  or  on  the  summits  of  the  peaks,  after  studying  his 
manual,  let  the  student  get,  if  he  can,  some  published  geo- 
logical report  on  such  a  country,  such  as  those  of  the  U.  8. 
Geological  Survey,  abounding  in  illustrations  and  geologi- 
cal sections.  Let  him  take  this  book  in  hand  and  go  to  the 
very  place  described  and  pictured  as  a  geological  section, 
and  with  his  hammer  study  each  member  of  the  section 
closely.  This  will  make  him  familiar  with  the  different 
geological  periods,  formations,  rocks,  minerals,  and  fossils, 
as  they  actually  appear  in  nature  rather  than  as  his  imagina- 
tion has  supposed  them  to  be  from  his  study  of  the  text  books : 
book  geology  and  field  geology  are  not  always  in  perfect 
harmony. 

Having  studied  and  learned  one  local  section  well,  such 
as  that  cut  by  a  stream  along  the  foothills  of  a  mountain 
range,  let  him  repeat  the  course  at  the  other  and  more  dis- 
tant points.  He  vill  find  at  each  locality,  though  the  main 
features  are  the  same,  there  is  always  an  interesting  variety, 
such  as  new  fossils,  peculiar  minerals,  changes  of  dip, 
faults,  or  other  structural  peculiarities. 

Along  the  flanks  of  a  mountain  range,  a  prospective  pros- 
pector cannot  study  too  many  of  these  geological  sections. 
Having  become  familiar  with  these  foothill  sections,  he  is 
prepared  to  plunge  into  the  heart  of  the  range  itself.  At 
first,  and  for  long  distances  perhaps,  he  will  encounter  only 
granitic  rocks  forming  the  axis  and  core  of  the  range. 
These  are  well  worthy  of  study  and  full  of  variety.  Later 
the  canyon  may  open  into  some  mountain  valley  or  park, 
where  the  strata  he  studied  on  the  foothills  or  prairie 
border  are  again  repeated  and  he  finds  himself  again  at 
home.  Seizing  upon  some  well-defined  and  familiar  repre- 
sentative of  a  geological  horizon,  from  this  as  a  standpoint 
he  soon  reads  off  the  succession  of  the  rest.  Here,  how- 
ever, the  appearance  and  texture  of  the  rocks  will  probably 
be  different  to  what  they  were  in  the  foothills.  Heat  has 
so  changed  or  metamorphosed  the  sandstones  and  shales 
that  they  are  scarcely  recognizable  as  the  same  rocks  as 
those  of  the  foothills.  Yet  even  here  a  highly  silicified 
fossil  shell,  or  a  leaf  impression  on  shales,  or  sandstones 
changed  into  slates  or  quartzite,  will  give  the  prospector 
his  clue  and  his  desired  and  definite  geological  horizon,  and 


«9 

he  will  have  little  difficulty  in  again  arranging  and  group- 
ing correctly  the  rocky  series.  But  a  prospector  has  a 
"  practical  end"  in  view.  He  is  "  after  the  precious  metal," 
gold  and  silver,  not  after  "  pure  science'  or  "  fossils  or 
sich  " ;  what  practical  use  is  there,  he  may  ask,  in  this  same 
careful  study  of  geological  sections,  where  probably  there 
is  not  a  speck  of  ^old  or  silver?  Simply  that  minerals  and 
metals  of^economic  value,  such  as  gold  and  silver,  are  more 
frequently  found  in  the  rocks  of  certain  geological  periods 
than  in  others.  Locally  this  is  especially  true.  For 
instance,  nearly  all  the  silver-lead  deposits  of  Colorado  are 
found  in  j  certain  bed  of  limestone  not  over  two  hundred 
feet  thick,  to  be  found  only  in  one  geological  period  out 
of  many  others,  viz. :  the  lower  division  of  the  Carboni- 
ferous. It  would  naturally  then  be  advisable  for  a  Colorado 
prospector  to  be  able  surely  to  identify  this  limestone,  as 
well  as  the  geological  horizon  in  which  it  occurs,  among 
the  various  other  limestones  of  various  other  periods  and 
ages  in  the  mountains. 

Again,  gold  is  mainly  confined  to  crystalline  rocks  of 
Archaean  age  or  to  porphyries  associated  with  these.  A 
prospector  should  be  familiar  with  these  rocks  and  their 
varieties.  Gold  is  also  found  in  the  placers  derived  largely 
from  the  breaking  up  of  these  rocks ;  the  ability  to  distin- 
guish the  different  pebbles  may  lead  to  the  source  whence 
the  gold  was  derived.  Familiarity  with  rocks  of  all  kinds 
is  a  necessary  prospector's  education  in  itself. 


GEOLOGICAL   SECTIONS  OF  COLORADO. 

In  illustration  of  what  we  have  said,  let  us  take  the  two 
engraved  generalized  sections  showing  all  we  know  of  the 
crust  of  the  earth  as  exposed  in  Colorado.    Plates  I  and  II. 

Plate  I  is  a  vertical  section  of  an  ideal  cliff,  showing  all 
the  members  of  the  various  periods  in  a  stupendous  cliff 
resting  on  fundamental  Archaean  granite  at  the  bottom  of 
a  canyon.  Plate  II  represents  the  same  rocks  and  succes- 
sion of  strata  displayed  in  upturned  "  hog  backs"  along  the 
flanks  of  the  mountains  and  foothills  on  the  border  of 
mountain  and  prairie.  Both  of  these  are  ideal  sections 
"  generalized"  or  "  made  up"  of  actual  partial  typical  sec- 
tions found  in  different  localities  in  Colorado,  the  vertical 


80 


one  in  detached  and  sometimes  widely  separated  districts 
in  the  heart  of  the  mountains;  the  other  at  similarly  dis- 
tinct and  different  localities  along  the  banks  of  the  various 
rivers  issuing  from  these  canyons  in  the  mountains,  cutting 
their  way  through  the  upturned  strata  of  the  flanking  foot- 
hills and  debouching  on  the  prairie. 

It  is  very  rare  to  find  at  one  locality  anywhere  in  the 
world  a  complete  section  of  the  earth's  crust  exposed. 
The  nearest  approach  to  this  in  Colorado  is  the  remark- 
able section  between  Colorado  Springs  and  Manitou,  which 
shows  along  the  wagon  road  the  succession  of  strata  from 
Archsean  to  Quaternary. 

One  of  the  most  remarkable  vertical  sections  in  the  world 
is  in  the  grand  canyon  of  the  Colorado  River,  where  the 
stupendous  cliffs  show  in  one  face,  a  thickness  of  some 
6,000  to  7,000  feet  of  strata,  representing  several  geological 
periods,  but  by  no  means  a  complete  section  of  all  that  is 
known  of  the  earth's  crust. 

To  show  how  dilBcult  and  rare  it  is  to  get  a  complete 
section  of  all  the  periods  in  the  earth's  crust,  we  may  state 
that  sometimes  the  rocks  of  a  single  geological  period  are 
from  10,000  to  20,000  feet  thick.  A  canyon  might  thus  be 
cut  to  a  depth  of  5,000  feet,  and  yet  be  in  only  part  of  a 
single  earth-period. 

By  far  the  most  extensive  and  available  sections  are,  like 
those  represented  in  the  engraving,  along  the  courses  of 
streams  on  the  flanks  of  a  mountain  range.  It  would  be  a 
formidable  task  to  scale  a  clifl  5,000  feet  high  and  examine 
minutely,  in  ascending,  each  of  its  geological  divisions; 
whilst,  on  the  other  hand,  in  the  foothill  regions,  a  pros- 
pector may  walk  over  and  mark  and  study  as  much  as  10,000 
to  40,000  feet  of  strata  along  the  banks  of  a  river  in  a  single 
afternoon.  In  the  Weber  Canyon  in  Utah,  as  much  as 
40,000  feet  of  strata,  composing  the  flanks  of  the  Wahsatch 
Range,  can  be  seen  by  the  traveler  from  the  windows  as  he 
glides  through  in  the  railway  car,  and  the  inquiring  pros- 
pector or  geologist  can  examine  and  study  this  vast  section 
leisurely  on  his  mule  or  on  foot,  without  doing  any  climb- 
ing and  on  a  good  road.  Smaller  partial  sections  can  be 
similarly  studied  along  many  of  the  streams  issuing  from 
the  Rocky  Mountains  among  the  foothills  of  Colorado. 
Such,  for  example,  as  at  Boulder  Creek,  Clear  Creek,  Bear 


I 


Plate  II. 

Generalised  Seotioa  of  Rocky  MonnUina  in  Colorado.     Showing  Economic  Proi 


Foothilh    and  //og^acA 


^toup 


fMf 


^K. 


Tdble   Lands 


i^V. 


Plains 

— ~V"" 


Plate  II. 

Iiowing  Economic  ProducU  in  Different  Geolofrical  Horisons  and  Strata. 


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Creek,  the  Platte  River,  and,  most  complete  of  all,  the  one 
along  Fountain  Creek,  near  Colorado  Springs,  which  we 
have  already  mentioned.  Similar  sections  can  be  found  in 
most  mountain  regions,  such  as  the  Adirondacks  in  the 
East,  and  the  Sierra  Nevada  and  Coast  Range  in  the  West 
of  America.  We  emphasize  again  that  the  close  study  uf 
these  is  the  best  preliminary  step  we  know  of  in  a  pros- 
pector's geological  education.  Let  us  now  examine  our 
ideal  generalized  Colorado  section,  which  we  will  suppose 
to  be  all  exposed  along  the  banks  or  canyon  of  a  single 
river.  We  will  start  from  the  Archaean  granite  in  the 
canyon,  thus  giving  us  a  sure  and  known  and  lowest  pos- 
sible geological  horizon  to  begin  with. 

THE  ARCHiHAN. 

This  Archaean  we  find  to  be  composed  toward  its  core, 
of  solid,  shapeless  (amorphous)  crystalline  granite,  which 
seems  to  have  been  fused  out  of  all  shape  by  water  and  fire, 
or  aqueo-igneous  fusion.  With  this,  but  more  characteristic 
of  the  upper  and  outer  edge  of  the  Archaean,  the  granite 
assumes  a  more  stratified  and  bedded  character,  which  we 
designate  as  "  gniess"  and  interbedded  with  it  at  intervals 
are  distinctly  laminated  or  finely  leafed  strata,  called  schist : 
all  these  varieties  are  composed  of  the  same  minerals  in 
different  arrangement  and  quantity,  viz.,  mica,  quartz, 
hornblende,  and  feldspar.  As  these  rocks  are  semi-igneous 
or  metamorphic,  we  find  no  fossils  in  them.  Traversing  all 
these  Archaean  rocks  and  cutting  them  at  all  sorts  of  angles, 
we  may  notice  some  eruptive  dykes  of  porphyry,  which 
were  once  certainly  molten  and  have  ascended  in  that  state 
through  fissures  opened  in  the  rocks  from  depths  and 
sources  unknown.  As  we  approach  the  edge  of  the  granite 
we  may  even  see  some  of  thess  molten  rocks,  insinuating 
once  fiery  tongues  among  the  weak  places  and  bedding 
planes  of  the  overlying  sedimentary  strata,  as  represented 
in  the  diagram,  where  one  dyke  is  shown  to  have  sent  out 
so  thick  an  intrusive  sheet  of  porphyry  (see  Plate  II  ) 
between  the  overlying  limestones,  that  where  subsequent 
erosion  took  place,  this  thick  sheet,  by  its  superior  hard- 
ness, was  left  to  form  the  highest  cap  of  the  mountain,  as 
on  many  of  our  prominent  mountain  peaks  such  as  Mt.  Lin- 
coln and  others  in  South  Park. 


Besides  these  rocks,  the  prospector  will  observe  numbers 
of  quartz  and  pink  feldspar  veins  of  all  sizes,  some  mere 
streaks  and  occupying  incipient  fissures  or  weak  places 
(veins  of  segregation),  others  occupying  large,  well-defined 
fissures  or  jointing  planes  (so-called  true  fissure  veins). 
Some  of  these  may  or  may  not  carry  metal,  gold  or  silver, 
lead  or  copper ;  at  any  rate  he  will  pay  them  especial  atten- 
tion, particularly  if  any  of  them  look  at  all  decomposed  or 
rusty,  or  are  in  close  proximity  to  an  eruptive  porphyry 
dyke. 


THE   CAMBRIAN. 

Now  the  prospector  emerges  from  the  Archaean  granite 
and  finds  the  first  true  sedimentary,  water-formed  rocks 
lying  where  the  ancient  seas  placed  them,  on  the  eroded 
upturned  edges  of  the  granitic  series. 

If  this  section  should  be  near  the  plains  or  foothills,  this 
first  sedimentary  rock  will  be  a  sandstone,  pure  and  simple, 
or  a  conglomerate  of  little  pebbles,  but  in  the  parks  and 
centre  of  the  mountains  where  these  ancient  strata  are  most 
conspicuous,  the  first  rock  lying  on  the  granite  is  a  hard, 
white,  semi-crystalline  quartzite  or  metamorphosed  sand- 
stone. He  may  possibly  find  some  obscure  signs  of  ancient 
fossil  shells  in  this  series,  which  is  called  the  Cambrian  now, 
though  formerly  it  was  held  to  be  only  a  lower  division  of 
the  Silurian.  In  Colorado  these  Cambrian  rocks  rarely 
exceed  200  or  300  feet  in  thickness,  but  in  other  regions 
they  are  often  very  much  thicker.  In  this  series  the  pros- 
pector may  look  for  precious  ore,  more  especially  gold.  He 
will  carefully  look  also  for  intrusions  of  eruptive  porphyry 
in  this  series,  as  at  the  junction  of  this  with  the  quartzite, 
ore  is  most  likely  to  be  found.  He  will  also  observe  any 
rusty  signs  filling  cracks,  as  good  indications  of  gold-bear- 
ing ore.  Silver  also  may  be  found  associated  with  lead  or 
zinc. 


,  f., 


SILURIAN. 


Walking  along,  he  next  comes  to  some  200  or  300  feet  of 
drab-yellowish  or  light  gray  thin  bedded  limestone  of  a 
dolomitio  character,  characterized  by  numbers  of  little 
white  flints  or  (rarely  in  Colorado)  by  some  fossil  shells. 


9$ 

which,  by  reference  to  the  engravings  in  his  manual,  he 
finds  to  be  Silurian,  and  so  recognizes  the  series.  Here  be 
may  find  indications  of  lead,  silver,  or  other  ores,  but  not 
much  gold,  as  a  rule. 

CARBONIFEROUS. 

The  next  series  of  this  should,  according  to  the  text-books, 
be  the  Devonian,  characterized  by  fossil  fishes  and  "  Old 
Red'  sandstones;  but  the  rocks  of  this  epoch  for  some 
reason  are  missing  in  Colorado.  Instead  of  this,  resting  on 
the  Silurian,  he  finds  a  thick  bed  of  heavy-bedded,  massive. 
"  blue-grey"  limestom^.  characterized  by  black  flints,  and  at 
rare  intervals  by  fossil  shells  and  corals,  which  again,  by 
reference  to  his  book,  he  finds  to  be  characteristic  of  the 
Lower  Carboniferous.  This  limestone,  when  traversed  by 
sheets  of  eruptive  porphyry,  has  yielded  at  Leadville  and 
at  Aspen  and  New  Mexico  and  Arizona  some  of  the  largest 
silver-lead  deposits  in  the  West.  In  fact,  throughout  the 
West  it  may  be  considered  as  the  main  silver-lead  horizon. 
This  limestone  is  generally  between  200  and  300  feet  in 
thickness  and  readily  recognized  by  ?*s  position  relative  to 
the  Silurian  below  it.  and  the  massiveness  of  the  strata  and 
their  dark  gray  color.  It  is  commonly  called  the  "  Blue 
Limestone"  in  Colorado. 


MIDDLE   CARBONIFEROUS. 

Next  on  this  is  a  bed  of  dark  black  shales  in  which  thin 
seams  are  sometimes  found,  and  fossil  plants  like  those  in 
the  coal  strata  of  Pennsylvania,  sufficient  to  show  that  it. 
loo.  belongs  to  the  Carboniferous.  This  is  followed  by 
some  2.000  or  more  feet  of  "grits,"  rough,  hard,  gritty 
sandstones,  partially  changing  into  quartzite.  akin  to  the 
"  mill-stone  grits"  of  the  Eastern  States.  A  few  limestones 
occur  in  this  thick  Middle  Carboniferous  series,  which 
locally,  when  capped  by  porphyry,  produce  silver-lead 
deposits;  but  generally  speaking,  the  "  grits"  are  unproduc- 
tive in  Colorado. 

The  Upper  Carboniferous  consists  of  beds  of  gypsiferous 
shale  and  heavy,  brownish-red  conglomerate  sandstones. 


«4 


TRIASSIC   "RED-BEDS. 


From  these  we  pass  into  a  series  of  heavy-bedded,  coarse 
conglomerate  sandstones  of  a  brick-red  color,  commonly 
known  as  the  "  Red-Beds"  in  Colorado ;  little  indications  of 
ore  are  to  be  expected  in  this  series.  The  prevailing  red- 
ness  of  the  series  makes  it  an  easily  recognized  geological 
horizon  in  Colorado  and  elsewhere.  The  thickness  in 
Colorado  varies  from  i.ooo  to  2,000  feet. 


I 


I 


JURASSIC. 

Next,  the  prospector  comes  to  a  softer  and  more  varie- 
gated series,  consisting  largely  of  pink,  green,  red,  or 
maroon  marls  and  clays,  with  some  thin  limestones  and  red 
sandstones.  This  is  the  Jurassic  series,  in  which  some 
remarkable  lizard  remains,  called  Dinosaurs,  have  been 
found,  proving  the  correctness  of  its  Jurassic  name.  This 
is  not  a  likely  mineral  horizon,  generally  speaking,  in 
Colorado. 

CRETACEOUS. 

These  softer  beds  are  capped  by  a  hard  massive  sand- 
stone about  200  feet  thick,  forming  by  reason  of  its  superior 
hatdness  a  prominent  hog-back  in  the  prairie  or  foothill 
region.  Fossil  remains  of  leaves  show  it  to  be  a  land  and 
fresh-water  group,  which  is  called  the  Dakotah  group. 

This  group  in  Colorado  forms  the  base  of  the  great 
Cretaceous  system;  lying  on  it  is  an  enormous  thickness 
of  drab  shales  with  a  few  limestones  characterized  by  fossil 
sea-shells,  showing  the  group  to  be  the  marine  Cretaceous, 
likewise  a  poor  prospecting-ground.  Toward  the  upper 
portion,  these  shales  pass  gradually  into  heavy-bedded 
sandstones,  containing  several  seams  of  coal  and  many 
impressions  of  tropical  foliage.  This  is  the  Laiamie  group 
of  the  Cretaceous,  evidently  of  fresh-water  origin,  and 
noted  as  the  main  coal-producing  horizon  in  Colorado  and 
the  West. 

TERTIARY. 

On  this,  at  a  somewhat  gentler  angle,  even  to  horizon- 
tality,  rest  thick  beds  of  shale  and  clay  and  conglomerate, 
composed  of  volcanic  detritus  and  pebbles,  showing  that  at 


«5 

the  time  these  Tertiary  beds  were  being  laid  down  by  large 
fresh-water  lakes  and  marshes  surrounded  by  tropical 
foliage,  volcanic  eruptions  on  a  grand  scale  repeatedly 
occurred.  Hence  it  is  that  many  of  the  Tertiary  beds  are 
preserved  from  erosion  by  beirg  capped  with  volcanic 
rocks,  such  as  basalt,  andesite,  or  rhyolite,  as  at  the  Table 
Mountains  at  Golden,  on  the  Divide  near  Colorado  Springs, 
and  elsewhere  in  Colorado.  One  of  these  lava-capped 
"mesas'  is  represented  in  the  section,  Plate  II.  Fossil 
leaves  and  coal-seams  are  found  in  this  period. 

QUATERNARY. 

Lastly,  strewn  indiscriminately  over  all  the  formations,  is 
the  "  Quaternary  drift,"  composed  of  loose  pebbles  and 
sands  and  clays,  the  material  derived  from  rooks  of  all  the 
periods  through  the  agency  of  glaciers  and  streams. 

Here  the  prospector  will  pan  for  his  gold  placer,  and  in 
his  search  may  possibly  come  across  the  teeth  or  tusks  of 
the  great  Mammoth  or  fossil  elephant,  together  with  the 
first  indications  of  the  presence  of  primitive  man.  The 
pebbles  by  their  variety  will  form  a  fertile  subject  of  study 
to  determine  to  what  class  of  rocks  they  belong. 

This  ends  the  prospector's  first  preliminary  lesson  in 
Colorado;  but,  taking  this  section  as  a  type,  he  may,  to  his 
great  advantage,  similarly  study  other  sections  far  remote 
from  Colorado. 

In  Colorado,  if  he  knows  this  section  by  heart,  he  has  the 
key  to  nearly  all  our  mountain  structure,  and  will  be  at 
home  wherever  he  goes.  He  will  be  struck,  too,  to  see  to 
how  small  a  portion  of  this  great  section  the  precious 
metals  are  more  or  less  confined,  principally  to  the 
Archaean  and  Paleozoic  rocks. 


CHAPTER  II. 


THE  PROSPECTOR'S  HISTORICAL  GEOLOGY. 

In  our  last  chapter  we  gave  some  hints  to  the  prospector 
how  to  commence  his  geological  studies,  and  gave  him  an 
example  of  a  geological  section  of  the  foothills  and  moim- 


26 

tains  of  Colorado,  and  how  to  study  it  in  detail  practically. 
Having  completed  this  study,  if  a  thoughtful  man,  he  will 
like  to  know  more  of  the  natural  history  of  all  this  section 
of  the  earth's  crust:  what  is  the  natural  history  of  the 
Archaean,  the  Cambrian,  Silurian,  etc.,  why  do  some  of 
these  strata  contain  sea-shells,  and  others  land-plants,  why 
are  some  evidently  of  marire,  and  o  lers  of  fresh-water 
origin,  and  particularly  why  are  some  especially  metal- 
liferous, and  others  not  so  much  so?  We  propose,  there- 
fore, in  this  chapter  to  give  him  a  brief  sketch  of  the  earth's 
history  as  exemplified  in  the  section,  Plates  I  and  II. 


\\\ 


HYPOTHETICAL   ORIGIN   OF   THE   EARTH. 

The  world  was  not  "  spoken  into  existence  ready  made" 
in  the  state  we  now  find  it.  It  has  attained  this  condition 
through  a  multitude  of  gradual  changes  and  revolutions 
which  have  taken  millions  of  years  to  accomplish.  The 
remote  history  of  the  earth's  origin  is  a  matter  of  hypothe- 
sis and  speculation.  There  are  reasons  for  supposing  that 
at  one  time  its  elements  were  in  a  gaseous  condition,  and 
that  this  planet  was  an  incandescent  luminous  cloud  revolv- 
ing through  space,  gradually  consolidating  into  a  molten 
ball  surrounded  still  by  an  atmosphere  of  gases,  a  condition 
perhaps  not  very  unlike  that  of  the  sun,  whose  interior  by 
some  is  supposed  to  be  passing  into  the  molten  state,  while 
its  exterior  consists  of  various  incandescent  gases  arranged 
more  or  less  according  to  their  specific  gravities.  The 
spectroscope  has  detected  the  elements  of  some  of  our  earth 
metals  and  minerals  in  the  sun  in  a  state  of  vapor.  The 
ultimate  source  of  the  precious  metals  is  again  a  matter  of 
speculation,  like  the  nebular  hypothesis  we  have  alluded  to, 
by  which  the  earth,  as  we  have  said,  is  supposed  to  have 
arrived  at  its  present  condition  as  the  result  from  the 
gradual  cooling  of  an  incandescent  mass ;  and  as  the  specific 
gravity  of  the  crust  is  much  less  than  that  of  the  whole 
mass  of  the  earth  it  has  been  inferred  that  the  heavy 
metals  must  be  in  much  larger  proportion  in  the  interior  of 
the  earth  than  in  the  rocky  crust,  though  this  greater 
interior  specific  gravity  might  be  also  accounted  for  by  the 
rocks  of  the  interior  being  much  more  tightly  packed  by 
enormous  pressure  than  those  near  the  surface.     Volcanic 


«7 

emanations  and  hot  springs  contain  metallic  minerals:  so 
also  do  the  waters  of  the  ocean.  But  we  know  not  from 
what  depth  the  former  came,  nor  from  what  source  the 
latter  derived  them.  As  circulating  waters  take  up  and 
throw  down  their  metallic  contents  under  varying  condi- 
tions, the  same  material  may  have  been  deposited  more 
than  once,  and  in  more  than  one  form,  since  it  reached  the 
rocky  crust. 

Upon  the  cooling  of  the  ball,  a  crust  formed  like  that  on 
molten  iron,  crumpled  and  corrugated  by  contraction,  due 
to  cooling,  into  an  uneven  surface,  with  comparatively 
slight  elevations  and  depressions,  and  doubtless  broken 
through  here  and  there  by  great  fissures  and  volcanic 
craters,  through  which  the  molten  flood  beneath  poured 
out  in  volumes,  adding  to  the  thickness  of  the  congealing 
crust. 

Upon  such  a  surface  the  gaseous  atmosphere,  gradually 
cooling  and  condensing,  descended  as  hot  chemical  rain, 
and  filled  the  troughs  of  the  crumpled  surface  with  a  hot, 
chemical,  steamy  ocean.  Whatever  land  of  primitive  lava 
rose  above  this  ocean  was  battered  by  the  waves,  reduced 
to  sediment,  and  deposited  as  the  first  sedimentary  strata 
in  the  bed  of  that  primaeval  ocean,  the  eruptions  from 
below  the  thin  crust  doubtless  contributing  largely  to  the 
same  material. 

ARCHAEAN   AGE. 

Thus,  perhaps,  were  formed  the  first  stratified  rocks  of 
the  world,  which  we  have  an  opportunity  of  actually  seeing 
and  studying,  viz. :  the  granitic  series,  with  its  varieties 
of  gneiss,  schist,  syenite,  etc.,  and  as  this  is  the  beginning 
age  so  far  as  we  know,  we  call  it  the  Archaean,  the  Greek 
for  beginning.  It  would  seem  probable,  however,  that 
these  granitic  rocks  forming  the  axes  of  our  mountains 
may  not,  at  least  in  part,  have  been  the  very  first  rocks  of 
the  crust,  for  we  observe  some  of  them,  such  as  the  gneisses 
and  schists,  to  be  stratified,  and  to  show  elements  in  them 
seemingly  derived  from  other  and  still  older  rocks,  which 
latter  may  or  may  not  have  belonged  to  the  original  cooling 
crust.  Some  geologists  claim  that  the  Archaean  is  the  first 
cooled  crust  and  attribute  it  to  a  molten  origin.  This  may 
be  true  for  the  seemingly  fused  massive  amorphous  granites 


28 

(though  these  may  be  but  the  result  of  aqueo-igneous  fusion 
of  sediment  or  extreme  metamorphic  action),  but  scarcely 
for  the  stratified  gneisses  and  schists,  though  it  is  to  be 
noted  that  a  sort  of  stratified  or  schistose  structure  is  some- 
times observed  in  truly  igneous  rocks  and  may  be  induced 
by  peculiar  arrangement  of  minerals,  pressure,  and  cleav- 
age, instead  of  water  lamination. 

The  subject  is  a  difficult  one  and  too  abstruse  for  the 
limits  of  this  work. 

In  the  scale  of  geological  periods  in  the  text-books,  we 
sometimes  find  this  great  Archiean  divided  into  two  or  more 
groups,  such  as  the  Laurentian,  Huronian,  and  of  late  the 


Plate  III. 

Archaean  Rocks. 

Algonkian.  The  Laurentian  is  the  oldest  and  may  be 
called  the  Archaean  proper,  whilst  the  Huronian  and  Algon- 
kian  may  be  grouped  generally  as  Pre-Cambrian,  or  series 
of  rocks  laid  down  after  the  Laurentian  and  before  the  Cam- 
brian. All  the  rocks  are  of  a  highly  crystalline  order  and 
have  a  peculiar  and  distinct  general  appearance,  different, 
as  a  rule,  to  those  of  any  subsequent  geological  periods  and 
so  not  easily  mistaken  for  them,  consisting  in  the  lower 
division  mainly  of  granite,  gneiss,  and  schists,  and  in  the 
upper  divisions  of  gneisses,  schists,  quartzites,  slater.,  some 
marble,  serpentine,  etc.  The  upper  or  Pre-Cambrian  series 
is  not  nearly  so  universally  found  as  the  Laurentian  or 


«9 


Archaean  proper.  In  Colorado  we  find  the  Pre-Cambrian 
represented  locally  in  South  Boulder  and  Coal  Creek  can- 
yons, along  the  foothills,  also  near  Salida  in  the  Arkansas 
valley,  in  the  Quartzite  range,  and  on  the  road  between 
Ironton  and  Ouray  in  the  San  Juan  Mountains.  The  new 
Koo^-o.nie  silver-mining  district  of  British  Columbia  seems 
to  be  largely  in  these  Pre-Cambrian  rocks.  This  Pre-Cambri- 
an is  usually  very  thick,  numbering  many  thousands  of  feet. 

It  is  distinct  from  the  Archaean  proper  or  Laurentian  by 
lying  on  the  latter  at  a  different  angle,  in  other  words 
"unconformable."  The  rocks,  too,  do  not  contain  so  much 
of  the  heavy  massive  granites  and  heavy-bedded  gneisses 
as  the  Laurentian,  but  are  more  characterized  by  quartzites, 
by  conglomeratic  gneisses  and  schists,  and  show  clearly 
that,  though  highly  metamorphosed  and  crystalline,  they 
are  of  true  fragmental  and  aqueous  origin,  for  the  pebbles 
in  the  gneiss  are  often  very  distinct,  and  ripple-marks  are 
not  uncommon  on  the  quartzites  and  slates  and  schists. 
The  material  was  doubtless  derived  by  waters  from  that  of 
the  underlying  and  older  Laurentian.  The  whole  Archaean 
series,  however,  has  evidently  passed  through  an  ordeal  of 
heat,  such  as  is  called  aqueo-igneous  heat,  and  all  its  ele- 
ments are  in  a  highly  crystalline  condition.  Its  strata  are 
intensely  folded  and  crumpled.     See  Plate  III. 

Signs  of  life,  in  the  upper  series  even,  are  exceedingly 
obscure  and  doubtful,  such  as  graphite  and  possibly  corals. 
Great  iron-beds  also  occur,  indirect  proofs  perhaps  of  the 
previous  existence  of  life. 

We  have  been  thus  particular  with  this  Archaean  Age, 
because  its  rocks  are  of  great  importance  to  the  prospector, 
being  the  main  repositories  of  gold,  silver,  and  the  precious 
metals  throughout  the  world.  Moreover,  many  of  the  other 
and  newer  rocks  containing  gold  and  silver  have  been  made 
from  the  detritus  of  this,  and  the  gold  placer-beds  largely 
from  the  detritus  of  the  rocks  and  porphyries  found  in  this 
age.  Thus  the  Archaean  may  be  considered  as  the  parent 
of  nearly  all  the  other  rocks.  When  later  we  have  studied 
the  origin  of  ore  deposits,  we  shall  see  how  eminently  the 
Archaean  Age,  with  its  attendant  heat,  chemical  reactions, 
fissuring,  metamorphism,  and  volcanic  eruptions,  was  favor- 
able to  the  diffusion  and  concentration  of  precious  ores  in 
its  rocks. 


JO 


CAMBRIAN   AND  fSlLURIAN   AGES. 

Cooling  and  consequent  contractions  still  progressing 
in  the  globe,  fresh  and  greater  wrinkles  and  corrugations 
were  caused  on  the  surface  of  its  crust,  and  some  of  these 
granite  sea-bottom  strata  were  crumpled  up,  till  the 
crumples  arose  above  the  then  universal  ocean  as  low 
islands  or  reefs.  The  ocean  had  by  this  time  cooled  suffi- 
ciently to  support  low  forms  of  marine  life,  and  so  along 
the  flanks  of  these  gigantic  islands  corals  formed  re^efs, 
shell-fish  swarmed  and  sea-weeds  grew.  Sands  formed  by 
the  waves  from  the  material  of  the  granite  were  laid  down 
as  shore-line  beacheS;  often  mixed  with  shells;  and  in 
djeper  water  corals  were  forming  limestones  as  at  the 
present  day,  both,  by  time  and  pressure,  consolidating  into 
hard  rock,  eventually,  it  may  be,  metamorphosed  by  heat 
into  a  semi-crystalline  hardness,  as  in  the  case  of  the  Cam- 
brian quartzite  and  Silurian  limestones,  the  latter  some- 
times changed  to  marble.  If  these  Cambrian  quartzites 
were  formed  from  the  detritus  of  the  granite  and  the  gra- 
nitic series  is  the  source  of  gold,  it  is  not  surprising  that  we 
find  the  Cambrian  quartzites  locally  rich  in  gold,  as  they 
were  the  auriferous  sea-beaches  (like  those  of  to-day  in 
California  which  are  gold-bearing)  of  that  period,  later 
consolidated  into  hard  rock.  In  Colorado  the  Cambrian 
quartzites  are  only  locally  prolific  in  gold,  as  at  Red  Cliff, 
but  as  they  have  hitherto  been  much  overlooked  by  pros- 
pectors they  are  worthy  of  closer  attention  by  the  gold- 
seekers.  The  limestone  not  being  of  a  true  fragmental 
origin,  but  formed  by  the  slow  work  of  corals,  could  not  be 
expected  on  consolidation  to  be  a  recipient  of  gold,  but 
later  by  its  peculiar  chemical  composition,  of  which  we  will 
speak  hereafter,  and  by  its  cavernous  nature,  it  furnished  a 
more  convenient  receptacle  for  silver  and  lead  ores. 

So  then  in  Colorado  and  in  other  regions,  we  find  first 
the  upheaved  crumpled  granite  of  the  old  Archaean  island, 
and  on  these  the  Cambrian  sandstone  or  quartzite  beach  of 
"  golden  sands"  with  some  fossil  shells.,  and  upon  this  again 
Silurian  limestone  with  relics  of  fossil  corals  and  shells. 
So  we  call  these  ages  the  Cambrian  and  Silurian,  because 


3« 

the  fossil  shells  and  corals  arc  peculiar  to  those  ages  and 
distinct  from  those  of  later  periods  or  the  present  clay. 

North  America  at  the  beginning  of  these  ;K'riods  was 
barely  outlined  by  a  few  granite  islands  congregating 
mainly  in  the  region  now  occupied  by  Canada,  whilst  one 
or  two  reefs  or  scattered  cLains  of  islands  marked  the  sito 


Plate  IV. 

America  at  Close  of  Archaean. 

of  the  Eastern  ranges  of  mountains,  and  a  few  parallel 
granite  islands  outlined  the  site  of  the  principal  uplifts  of 
future  great  ranges  of  the  Western  Cordilleras.  All  else 
was  ocean,  and  that  ocean  was  depositing  its  Cambrian 
beaches  and  Silurian  coral  limestones  against  or  near  these 
granite  islands,  destined  in  time  to  grow  into  lofty  moun- 
tain ranges  and  to  become  the  backbone  of  the  American 
Continent.     See  Plate  IV. 


DEVONIAN. 


The  Devonian,  which  should  come  next  in  order  in  the 
geological  tree,  appears  to  be  absent  in  Colorado,  but  is  well 


shown  at  the  Eureka  Mines  in  Nevada.  The  rocks  appear 
to  be  mostly  marine  limestone  full  of  corals  and  shells  and 
a  few  remains  of  gigantic  fishes,  for  which  this  age  was  cele- 
brated. Land  plants  and  some  coal  are  found  in  it  in  the 
East.  Lead  silver  ores  may  be  expected  in  the  limestones 
of  this  age,  and  in  Cornwall  (England)  Devonian  slates 
traversed  by  quart/,  porphyries  arc  the  main  rocks  carrying 
tin  ore,  a  metal  very  scarce  at  present  in  North  America. 

These  ages  we  arc  speaking  of  are  separated  or  distin- 
guishable from  one  another  by  decided  and  characteristic 
changes  in  the  fossil,  animal,  and  vegetable  life  existing 


Arehman 


Cenozoic 


Plate  V. 

Section  Showing  Unconformity  of  GeoloRical  Bras. 


between  one  ap^e  and  another ;  also  in  some  countries  by 
marked  unconformability  of  the  rocks,  i.e.,  the  rocks  of 
one  age  lying  at  a  different  angle  upon  the  upturned  rocks 
of  a  previous  age,  marking  great  oscillations  between  sea 
and  land. 

In  America,  however,  these  oscillations  between  sea  and 
land  seem  to  have  been  i  ss  than  in  Europe,  and  we  find  a 
general  uniform  rise  of  the  continent  from  the  primitive 
oceans,  and  an  orderly  succession  of  strata  lying  against 
the  ?anks  of  the  ever-rising  granite  nucleus  of  both  moun- 
tains and  continent.  Hence  to  distinguish  the  different 
ages  we  are  driven  more  to  the  study  of  fossils  and  litho- 
logical  peculiarities  than  deriving  any  help  from  observed 
marked  unconformability.  See  Plate  V  ,  in  which  the  strata 
of  the  different  eras  lie  upon  one  another  at  different 
angles,  and  the  glacial  and  Quaternary  drift  pebbles  and 
clays  are  strewn  unconformably  also  over  the  tops  of  the 
uptilted  and  eroded  strata  of  all  the  eras  beneath. 


Si 


CARBONIFEROUS. 

In  the  Eastern  States,  as  the  American  continent  fi^radually 
rose  from  the  sea.  and  to  the  {granite  islands  had  been 
added  a  Cambrian.  Silurian,  and  Devonian  shore,  with 
further  unequal  elevation,  a  kind  of  wide  trough  or  syn- 
clinal fold  or  depression  appears  to  have  been  formed 
between  the  middle  and  eastern  part  of  America,  which 
was  at  first  occupied  by  a  wide  arm  of  the  sea.  later,  by 
continued  elevation,  by  a  great  body  of  fresh  water,  and 
later  by  low  marshes  and  low  marshy  islands  barely  ah'^ve 
sea-level.  Upon  these  low-lying  lands  grew  a  dense  \<n:i- 
tation,  unlike  any  of  the  present  day.  but  resembling  some- 
what the  tree-ferns  of  our  southern  semi-tropical  States. 
This  low-lying  region  was  subject  to  freshets  and  inunda- 
tions from  the  surrounding  higher  regions,  periodically 
deluging  the  swamps  and  swamp  vegetation  with  river  and 
flood  deposits  of  pebbles  and  sand,  under  pressure  of  which 
the  peat  gradually  turned  into  coal.  Successive  coal  seams 
were  formed  by  successive  growths  of  vegetation  between 
the  intervals  of  periodic  inundation  or  of  subsidence,  and 
possibly  at  times  of  upheavals,  for  these  low  lands,  as 
sediments  accumulated,  appear  at  times  to  have  sunk  below 
the  sea  and  again  to  have  been  either  built  up  above  it  by 
fresh  supplies  of  sediment,  or  to  have  been  temporarily 
raised  up  by  upheaving  forces. 

Finally,  by  a  grand  revolution  which  closed  the  Carbonif- 
erous age  in  America,  the  coal-swamps  with  their  coal-beds 
and  strata  were  crumpled  up  to  form  the  present  great 
Appalachian  Chain. 

Similar  movements  no  doubt  took  place  about  the  same 
time  in  the  Rocky  Mountain  and  Western  region.  But 
here  the  marine  condition  seems  to  have  predominated  over 
the  fresh  water  one,  for  we  find  the  Carboniferous  in  Colo- 
rado more  represented  by  marine  fossiliferous  limestones 
and  sandstones  than  by  those  of  fresh-water  origin,  though 
the  Weber-grits  may  have  had  a  fresh-water  origin,  as  in  a 
few  rare  instances  we  find  fossil  plants  like  those  in  Penn- 
sylvania together  with  a  few  insignificant  small  seams  of 
coal.  But  in  the  West  it  is  evident  that  the  circumstances 
from  one  cause  or  another  were  not  favorable  for  the  pra- 


duction  and  growth  of  extensive  coal-beds  as  in  the  Eastern 
States.  The  coal-forming  time  was  reserved  in  the  West 
for  a  much  later  period,  viz. :  the  Laramie  or  Upper  Creta- 
ceous. The  Lower  Carboniferous  in  Colorado,  however, 
contains  in  its  limestones  much  of  our  silver-lead  wealth,  as 
at  Leadville  and  Aspen. 

The  Cambrian,  Silurian,  Devonian,  and  Carboniferous 
Ages  have  been  grouped  together  by  geologists  into  one 
great  era,  the  Paleozoic,  owing  to  a  general  family  likeness 
in  the  fossil  fauna  and  flora  of  these  ages. 

To  the  Archaean  and  Paleozoic  rocks  the  bulk  of  our  veins 
and  deposits  of  gold  and  silver  are  mainly  confined,  though 
both  in  Colorado  and  elsewhere,  as  will  appear  later,  if 
certain  peculiar  conditions  are  present,  the  rocks  of  the 
later  and  newer  periods  may  also  in  some  regions  produce 
precious  ores.  But  the  prospector  should  give  his  closest 
attention  to  these  o/der  rocks;  hence  we  have  devoted  extra 
space  to  their  description  and  history. 


TRIASSIC   AND   JURASSIC,    OR  JURA-TRIAS. 

After  the  Carboniferous,  followed  the  Triassic  and  Ju- 
rassic; sometimes  in  America,  owing  to  the  difficulty  of 
positively  separating  the  two  periods,  they  are  combined 
under  one  name,  the  Jura-Trias,  and  in  Colorado  are  locally 
called  the  "  Red-Beds,"  owing  to  their  prevailing  red  and 
variegated  colors.  The  series  is  well  represented  in  the 
celebrated  Garden  of  the  Gods,  near  Colorado  Springs. 
The  red  conglomerate  sandstone  of  the  Trias  proper  has 
so  far  yielded  no  determinative  fossils,  but  the  variegated 
clays  in  the  upper  Jurassic  at  Morrison  and  elsewhere  have 
yielded  some  remarkable  Saurian  remains  of  land  lizards. 
It  is  probable  from  the  presence  of  salt  and  gypsum  in 
these  red-beds,  and  the  prevailing  redness  of  the  rocks,  due 
to  iron  which  was  not  leached  out  through  the  agency  of 
organic  life,  and  the  general  absence  of  fossil  remains,  that 
the  lower  portion  of  these  rocks  was  laid  down  in  land- 
locked salt  seas,  or  salt  lakes,  shunned  by  both  vegetable 
and  animal  life.  The  upper  portions,  however,  show  evi- 
dence of  the  existence  of  land  of  a  low  marshy  character, 
with  fresh  water  and  probably  large  estuaries,  as  we  find 
the  remains  of  turtles,  crocodiles,  fresh-water  shells,  and 


Dinosaurs  or  land  lizards.  The  rocks  of  these  periods  are 
not  generally  prolific  in  ores.  The  Silver  Reef  sandstone 
of  Utah  is  an  exception,  which  contains  chloride  of  silver 
disseminated  through  it.  When  pierced  by  eruptive  rocks, 
however,  ore  should  be  looked  for  in  this  series  as  else- 
where. 

CRiyiACEOUS    PERIOD.     . 

Upon  this  followed  the  Cretaceous,  a  series  of  very  thick 
formations,  numbering  several  thousands  of  feet  in  Colo- 
rado, consisting  in  its  middle  portion  of  limestones,  and 


Plate  VI. 


North  America  in  tlie  CretHceous. 


thick  beds  of  drab  shale.  These  are  mostly  marine,  as 
shown  by  the  sea-shells  in  them,  but  at  the  base  is  what  is 
called  the  Dakotah  group,  or  Cretaceous  No.  i,  a  prominent 
sandstone  hog-back  in  which  the  fossil  impressions  of  leaves 
very  like,  but  not  identical  with,  those  of  the  present  day 
show  that  land  and  fresh  water  existed  at  the  time.  The 
limestones  and  clays  of  the  middle  or  Colorado  group,  con- 
tain quantities  of  fossil  marine  shells,  yuch  as  the  Nautilus, 
Ammonite,  Baculite,  and  Inoceramus. 
The  Laramie  forms  the  v.pper  group  of  the  Cretaceous, 


36 


and  contains  our  principal  western  coal-fields  and  abounds 
in  fossil  remains  of  tropical  foliage. 

This  Laramie  group  marks  an  important  era  in  our  Rocky 
Mountain  region,  for  it  shows  that  beginning  of.  the  great 
Rocky  Mountain  revolution,  by  which  the  granite  islands 
before  mentioned,  against  which  all  the  previous  sediments 
had  been  forming,  mainly  beneath  the  sea,  were  elevated 
10,000  feet  or  more  into  continental  or  mountainous  masses, 
dragging  up  with  them  portions  of  the  sea  bottom  and 
exposing  it  as  land  surface,  draining  off  the  shallow  Creta- 
ceous sea  which  had  hitherto  divided  the  Eastern  half  of 
the  American  continent  from  the  Western,  bringing  on  a 
land  and  continental  condition,  which  was  completed  in 
the  following  Tertiary  age  and  has  continued  to  the 
present.     See  Plate  VI. 

The  Jurassic,  Triassic,  and  Cretaceous  are  grouped  into 
one  main  division  called  the  Mesozoic  or  middle-life  era  of 
the  world's  history.  None  of  the  rocks  of  this  age  in  Colo- 
rado are  celebrated  for  ore  deposits,  except  locally  under 
local  conditions. 

In  California  and  portions  of  the  extreme  West  where 
these  rocks  have  been  highly  metamorphobed  by  heat  and 
penetrated  by  igneous  rocks,  some  of  the  leading  ore 
deposits  of  gold  and  silver  are  found.  The  same  remark 
applies  also  to  the  succeeding  Tertiary  in  those  regions, 
particularly  in  the  Sierra  Nevada  and  Coast  ranges. 


TERTIARY. 

The  Tertiary  age  seems  in  the  Rocky  Mountains  to  mark 
an  era  of  comparative  rest  in  mountain  elevation,  for  the 
strata  forming  some  of  the  divisions  of  this  age  lie  almost 
horizontally  upon  the  tops  of  the  earlier  upturned  periods. 

These  beds  were  formed  by  fresh-water  lakes  in  Colorado 
surrounded  by  tropical  vegetation.  In  the  Coast  ranges  of 
California  the  Tertiary  is  upturned  into  mountain  forms 
and  metamorphosed,  and,  from  the  presence  of  sea-shells, 
is  clearly  of  marine  origin.  The  Tertiary  in  Colorado  is 
best  seen  in  outlying  table-lands.  In  Wyoming  the  Ter- 
tiary lake  formed  the  Green  River  beds  and  Bad  Lands 
abounding  in  fossil  mammals,  leaves,  fishes,  and  insects. 
The  Tertiary  was  the  world's  tropical  summer,  a  period  of 


.  ( 


37 

beautiful  lakes  of  semi-tropical  foliage  and  a  warm  cli- 
mate. In  certain  regions  it  was  disturbed  by  gigantic 
revolutions  which  upheaved  the  Himalayas  and  the  Alps. 
Such  revolutions  as  occurred  in  our  Western  Cordillera 
system  were  marked  by  enormous  ebullitions  of  lavas  of 
various  kinds  issuing  from  fissures  deluging  Idaho,  Nevada, 
part  of  Oregon,  and  Washington.  Remnants  of  this  same 
disturbance  are  seen  in  the  form  of  basaltic  overflows  cap- 
ping Tertiary  strata  in  Colorado  and  New  Mexico ;  and  the 
vast  volcanic  region  of  San  Juan  in  Southern  Colorado  is 
covered  with  successive  lava  overflows  of  the  saine  period. 
The  Tertiary  rocks  in  Colorado  are  not  generally  good 
prospecting  ground.  The  lavas,  however,  are  (with  the 
exception  of  the  basalt,  which  for  some  reason  is  generally 
sterile)  locally  productive,  as  for  instance  the  entire  San 
Juan  Region,  also  Cripple  Creek  Mining  Camps  and  Silver 
Cliff.  So  the  prospector,  whilst  he  need  not  waste  time 
among  the  sedimentary  beds,  will  do  well  to  examine  any 
eruptive  rocks  of  this  period  for  gold  especially,  and  also 
for  silver.  The  varieties  of  lava  are  principally  andesite, 
rhyolite,  trachyte  and  basalt.  In  the  Coast  range  of  Cali- 
fornia, where  the  Tertiary  beds  have  been  metamorphosed 
by  heat  into  slates,  gold  and  cinnabar  are  found. 


GLACIAL   EPOCH    AND   QUATERNARY   AGE.     • 

The  Tertiary  Summer  was  closed  by  the  world's  Great 
Winter.  The  ice  from  the  north  pole,  for  some  reason  we 
will  not  discuss,  extended  its  domain  far  south  to  latitude 
40.  All  the  northern  temperate  regions  of  the  world  were 
ice-sheeted  and  the  sheet  extended  itself  as  by  long  fingers 
down  the,  by  that  time,  highly  developed  mountains,  filling 
the  ravines  with  glaciers.  By  the  downward  destructive 
grinding  motion  of  the  glaciers,  the  ravines,  commenced  by 
water,  were  deepened  and  widened  by  ice.  Fissure-veins 
were  thus  exposed,  both  of  gold  and  silver.  The  debris 
from  their  progress  the  glaciers  carried  on  their  backs  and 
dumped  at  the  outlet  of  the  canyons ;  and  when  the  tem- 
perature finally  became  warmer  and  the  glaciers  melted, 
all  the  long  lines  of  traveling  boulders  scattered  upon  their 
backs,  many  of  them  containing  gold  robbed  from  the 
veins,  were  left  as  banks  or  "  moraines,"  forming  out  "  gold 


placer"  grounds  along  the  sides  of  our  streams  and  canyons, 
or  sometimes  a  thousand  feet  above  the  present  river-bed, 
marking  the  original  height  or  thickness  the  great  ice 
bodies  once  attained. 

So  were  our  canyons  largely  formed,  and  so  did  our  gold- 
placers  originate.  After  the  Glacial  Epoch,  a  warmer 
period  set  in,  called  the  Quaternary.  The  ice  melted. 
Vast  bodies  of  fresh  water  were  distributed  in  wide  streams 
and  monstrous  lakes  over  large  portions  of  this  hemisphere. 
The  rough  "  morainal"  dumps  of  the  glaciers  were  "  sorted" 
or  "  modified"  by  water,  rolled  into  pebbles  and  sand,  and 
redistributed  along  the  banks  of  streams  or  carried  out  into 
beds  of  lakes.  In  these  pebbles  and  sand  was  much  of  the 
precious  metal  mined  and  robbed  from  the  veins.  The 
gold  by  its  insolubility  remains  to  this  day  in  our  placer- 
beds  and  "  drift"  or  "  wash"  and  is  collected  by  hydraulic 
mining.  That  the  prospector  for  gold  should  closely  study 
these  Glacial  and  Quaternary  deposits  is  evident. 

So  ends  the  history  of  our  section.  Still  the  agencies  of 
nature  are  at  work  as  of  old.  Continents  are  gradually  ris- 
ing or  sinking.  Mountains  are  being  imperceptibly  ele- 
vated. Water  is  still  sculpturing  them  with  canyons. 
Rivers  are  carrying  down  fragments  robbed  from  the  land 
and  depositing  them  in  the  ocean  to  form  strata  for  future 
continents. 

The  fires  of  the  earth  are  not  yet  dead,  for  volcanoes  still 
vomit  lava.  The  earth,  however,  is  still  continuing  to  lose 
internal  heat.  Its  crust  is  still  contracting  and  wrinkling 
itself  upward,  for  we  find  modem  sea-beaches  raised  high 
on  our  seaboard  cliffs.  Shocks  of  earthquakes  from  time 
to  time  prove  that  motion  of  some  kind  is  going  on  beneath 
us,  and  doubtless  our  mountains  are  still  rising  impercep- 
tibly, as  they  appear  to  have  done  in  ages  past,  giving  addi- 
tional lifts  and  elevation  to  old  uplifted  strata,  and  slowly 
elevating  newer  strata  that  since  the  Tertiary  have  lain  ap- 
parently undisturbed.  We  say  apparently,  for  not  only  are 
the  Tertiary  beds  uplifted  from  five  to  ten  degrees,  but 
even  the  more  recent  Quaternary  deposits,  showing  that 
movement  has  been  going  on  comparatively  recently  and 
may  still  be  progressing  imperceptibly. 


39 


CHAPTER   III. 

THE  PROSPECTOR'S  PALEONTOLOGY  OR  STUDY  OF 

FOSSILS. 

A  prospector  in  his  roaming  among  the  rocks  is  likely 
from  time  to  time  to  come  across  a  good  many  fossils  or 
petrified  remains  of  life  that  once  existed  on  this  planet. 
He  will  feel  curious  to  know  what  these  are,  what  class  of 
animal  or  vegetable  they  may  represent,  to  what  geologi- 
cal era,  epoch,  or  subdivision  they  may  belong. 

Fossils  to  a  geologist  are  the  labels  of  the  rocks ;  show  a 
geologist  a  fossil,  and  he  will  probably  be  able  to  tell  at  a 
glance  whether  the  fossil  came  from  a  series  of  Paleozoic, 
Mesozoic,  or  Cenozoic  rocks;  whether  it  belonged  to  a  very 
ancient  geological  period  down  near  the  primitive  granite, 
or  to  a  comparatively  recent  one  near  the  modern  soil, 
high  up  in  the  geological  scale  and  nearer  to  the  life  of  the 
present  day.  He  may  be  able  to  tell  not  merely  whether 
it  belongs  to  one  of  the  great  divisions,  to  the  great  eras, 
but  also  to  the  subdivisions  of  these  eras,  whether  to  the 
Silurian  or  Carboniferous,  the  Jurassic,  or  the  Cretaceous, 
or  even  to  minor  divisions  of  these,  called  groups ;  whether, 
for  example,  it  belongs  to  the  Dakotah  group  of  the  Cre- 
taceous, or  to  the  Laramie  group  of  the  same  period. 

PRACTICAL   USE   OF    FOSSILS. 

The  practical  use  of  a  general  knowledge  of  fossils  is  ob- 
vious. A  prospector  finds  ifl  certain  strata  a  fern-leaf  of 
the  Carboniferous ;  this  tells  him  he  must  be  on  the  coal 
strata  and  forthwith  he  hunts  for  coal.  Or  he  finds  a 
Paleozoic  shell  or  coral,  which  points  to  the  fact  that  he  is 
probably  in  the  neighborhood  of  the  precious  ore-bearing 
rocks. 

Later  perhaps  he  finds  a  shell  or  coral  characteristic  of 
the  lower  Carboniferous  blue  limestone,  the  celebrated 
lead-silver  bearing  formation  of  Colorado  and  the  West, 
and  he  is  encouraged  to  look  for  these  ores.  The  lime- 
stone by  itself  is  but  a  poor  guide,  for  there  are  many  lime- 


^ 


40 


! 


stones  not  unlike  it  in  the  different  series  of  rocks,  but  this 
particular  shell  labels  tnis  as  "  the  blue  limestone"  and  no 
other.  Hence  a  characteristic  fossil  may  help  consider- 
ably in  following  up  in  its  extension  an  ore-bearing  rock, 
and  not  only  that  locally,  but  in  regions  very  far  apart. 
Soon  after -the  celebrated  ore  deposits  of  Aspen  were  dis- 
covered, and  the  mines  were  in  their  infancy,  some  fossils 
were  discovered  that  showed  the  deposits  to  be  in  the  same 
limestone  as  that  at  Leadville,  which  had  proved  there  so 
productive.  This  gave  an  additional  impetus  to  the  camp, 
"  a  second  Leadville,"  so  it  was  said. 

Again,  though  a  prospector  may  not  find  at  once  the  par- 
ticular geological  stratum  or  period  he  is  looking  for,  if  he 
finds  a  characteristic  fossil  anywhere,  in  some  other  period, 
he  knows  from  it  whether  the  period  he  is  after  lies  geo- 
logically below  or  above  where  he  is  looking. 

Thus,  if  a  prospector  finds  a  Silurian  shell  he  knows  that 
the  Carboniferous  "blue  limestone"  must  be  close  above 
this  Silurian,  or  if  he  finds  a  Marine  Cretaceous  shell,  he 
knows  that  the  Laramie  coal-bearing  group  lies  above. 
On  finding  a  Cretaceous  or  Jurassic  fossil,  he  knows  that 
the  Carboniferous  and  Paleozoic  series  must  lie  considerably 
below  him. 

In  the  accompanying  geological  table,  Plate  VII.,  we  have 
shown  what  rocks  and  what  minerals  and  metals  are  likely 
to  be  found  in  the  geological  divisions  and  subdivisions; 
also,  generally,  what  classes  of  fossil  life  are  to  be  expected 
in  each. 

Then  in  the  diagrams  of  fossils,  we  have  selected  pictures 
of  the  fossils  most  commonly  to  be  found  in  all  the  great 
divisions,  so  that  if  the  prospector  finds  a  fossil,  he  may,  by 
comparing  it  with  the  picture'^,  find  what  its  name  is,  and 
to  what  great  geological  division  or  subdivision  it  belongs; 
it  is  not  so  necessary  for  him  to  remember  the  scientific 
"  jaw-breaking"  names  of  these  fossils,  as  it  is  for  him  to  be 
able,  at  sight,  to  recognize  whether  it  belongs  to  one  or 
other  of  the  great  eras,  or,  better  still,  to  one  of  the  minor 
subdivisions  of  these ;  whether  it  is  Paleozoic  or  Mesozoic, 
whether  Silurian  or  Cretaceous,  whether  it  belongs  to  the 
Colorado  marine  Cretaceous  or  to  the  Laramie  fresh-water 
Cretaceous,  etc.  If  the  fossil  is  a  very  peculiar  one  and 
cannot  be  identified  as  belonging  to  any  of  the  common 


CHARAC7ERI5TIC  R0CK6.  MmML3,M£TALi$C        fOJ3/i3. 


Soil  cidj.pepoies 


dome  Gold 


Man,  Buttdio  8c. 


Ptbblcs  band. Clay 


PlacerGold 


lMS£l/ stratified 
CongimeratexSandi 

Sdialtjndssite 
miom  Lavd\ 
CongiomerdJes 
Sanditona 
dhale^  a  Cla^i 
ySome^mcanic 
detritus.ot/Knof 

Granitic  detritus 


Old  Gold  Placers 
inCalifornla 


.Gold  bearing 
/n  Califomia  also 
mhptialT 

in  Colorado 
andCalifornia 


Fo55il  Leai/€d 
Mammali 

in  California 
MarlneShelb 


CoH^Beds 
dand3tone5 
Drab.bhales.  Clay^ 

Limestone 
Darkonaies 

^tOBL 


larjaaMcm 


ReanirliX"— 
'me  zfone 


Coal 

Canon  Oty  Oil Horiion 
Flux  Lime 

ClayjrontStone 
rireciav 


Lin '         ' 


o/L 

Mi 


Gypsum 


LemsJimac. 
sea  yielis 

Japfiiles  Baculitu 

sea  Sire/is 

Inqceramus 

oyjren 

Leat^es  of  trees 


Thin  Ume6tone3 
TtiicKRedCongiomeiate 
sandstone 


'kfin^Sfone 


.Turner . 

SJhca  jor  GJasi 
J/fver  fieefJcMBbtone 
5cmeiMBuil(mStone 


Dinosaurs  Co/a 
^aS/reils/nH/^i/ig 


fboiprlnisotJaurians 


,  •  •  •  •  •  •  •  Kc 

L.Qrb\ 


Gypsiferous  Siiaies 

Ifedd/Jif  Conglomerate 

Eastern  Coal  Beds 

S^aiesJand^one^ 
Grit^  a  Stiale^ 


Blue  Limestone 


Caitem  Coat 
of  Pennsylvania 

Jiiyer  Lead 


Land  Plants 

,     Cordis  ^    ^ 
^Mijwiffrxetc. 


fieddisA  Sandstone 
Limestones 


fureka.  Nevada 
Silver  Lead 

*    Deposifs 


SeaSiieiis 
fist?  Cordis 


Drat)  Pate  Limestone 
Dolomite 


Marble 
Jilver.  Lead 

iron 


JeaSttelb 
Crustacea 
Triiolfites  Cordis 


Elates 
Quartzites 


Gold 


JeaMls 


»ecmaidmi/Mangfomiriric 
Gneisi.sctiist 
States.  Marble 


Granite.  Gneiss 
Sctiist.  syenite 


Gold.  Sliver 
LeadZincCofipergc 

Iron 


FetvPositiye 
J/^nsc^Ufe 


Plate  VII. 

Prospector's  Geological  Table  of  Western  Formations,  Showing  Principal 
Characteristic  Rocks,  Minerals  and  Fossils  to  be  Found  in  Them. 


4a 

ones  we  have  pictured,  he  had  better  send  it  to  the  office  of 
the  U.  S.  Geological  Survey  at  Washington,  or  to  some 
good  paleontologist.  We  frequently  have  fossils  sent  to 
us  to  know  whether  this  or  that  fossil  is  a  likely  indication 
of  the  presence  of  coal  or  other  mineral,  and  sometimes  our 
identification  is  a  material  help  to  the  prospector;  but  with 
the  above  table  the  prospector  could  save  himself  the  trouble 
and  postage-stamps. 

ARCH/EAN. 

Starting,  then,  from  the  Archaean  ns  a  sure  and  safe  hori- 
zon, the  prospector  will  find  no  fossils,  and  only  some  in- 


Plate  VIII. — Cambrian  Fossils. 

I,  a,  3,  Trilobites  ;  4,  Track  of  Crustacea  ;  5,  Track  of  Worm;  6,  7,  Sea  Shells. 

direct  probable  evidences  of  past  life,  such  as  graphite, 
which  may  possibly  represent  ancient  coal  derived  from 
some  form  of  vegetation  unknown  to  us.  Limestone  and 
marble  are  also  indirect  evidences  of  past  organic  life, 
most  modern  limestones  being  due  to  the  remains  of  corals, 
etc.  Whatever  life  may  have  existed  in  those  primitive 
granitic  rocks  has  been  pretty  well  obliterated  by  exces- 
sive metamorphism  and  crystallization  of  the  strata. 


A. 


43 


LAM  BK I  AN. 

Resting  on  the  granite  he  finds  the  "  Primordial"  or 
"  Cambrian"  series,  sometimes  called  the  Potsdam  Sand- 
stone. If  this  series  consists  of  unaltered  sandstones,  he 
may  be  fortunate  enough  to  find  some  of  the  shells  and 
other  traces  of  life  of  those  old  beaches  as  shown  in  the 
diagram,  but,  generally  speaking,  in  Colorado  and  the  West 


>> 
e 


Plate  IX. — Silurian  Fossils. 

1,  2,  Orthis  ;  3, 4,  Spirifer ;  5,  Pleurotomaria ;  6,  Murchisonia ;  7a,  7^,  Trilobite 
(Calyinene)  ;  8,  Coral  Fenestella  ;  9,  Coral  Chofitites ;  10,  Graptolite  ; 

II,  Orthoceratite. 

the  Cambrian  is  so  highly  metamorphosed  and  altered  into 
hard  crystalline  quartzites,  that  evidences  of  past  fossil  life 
are  as  scarce  and  indistinct  as  in  the  Archaean,  and  prob- 
ably for  the  same  reason  The  forms  he  may  find  are  a 
little  Crustacea  called  a  I'rilobite,  something  like  a  "  sand 
crab,"  also  a  few  little  shells  and  some  marks  of  worms. 
Plate  VIII. 


44 


SILURIAN. 

In  the  next  series,  the  Silurian,  he  may  be  more  fortu- 
nate. He  may  find  remains  of  sea-weeds,  corals  and  shells, 
and  fragments  of  a  sort  of  sea-worm  called  a  Crinoid,  or 
sea-lily.  The  little  discs  with  a  hole  in  the  centre  form- 
ing a  little  ring  about  the  size  of  a  pea,  constituting  the 
discs  or  rings  of  which  the  stems  of  the  sea-lily  are  com- 


Plate  X. — Devonian  Fossils. 

X,  Spirlfer;  2,  Comocardiuin  ;  3,  Orthis;   4,  Goniatites ;  5,  6,  7,  Corals  ;  8,9, 
10,  Fish  Teeth  ;  ii,  12,  Fish  Scales. 

posed,  are  sometimes  very  common  in  Silurian  and  Paleo- 
zoic rocks,  though  it  is  rare  to  find  a  complete  Crinoid,  and 
especially  the  beautiful  comb-like  flower  or  head  of  the 
sea-lily.  He  is  likely  to  find  also  a  more  advanced  type  of 
the  Trilobite  and  various  Spirifers  and  other  shells  as  pic- 
tured.    Plate  IX. 


45 


nEVr)NIAN. 

In  the  Devonian  he  may  find  the  teeth  or  bones  of  fisheA, 
and  a  lew  remains  of  peculiar  land  plants,  neither  of  which 
are  known  in  the  Silurian  below,  also  many  corals. 

CARBONIKEROUS. 

In  the  Lower  Carboniferous  "  blue  limestone,"  corals  and 
shells  appear,  especially  Spirifers  and  Productus.  together 


Plate  XI. — Carboniferous  Fossils. 

\a,  i/>,  ic,  Productus  ;  2,  2,  Spirifers;  3,  3,  3,  Rliynconella  ;  4,  Buumphalus  ;  5, 

5,  Crinoids  ;  6,  Pleurotomaria  ;  7,  Belleroplion  ;  8,  Athyris  Subtilita  ; 

Q,  Astartella;  10,  Ooniatites  ;  11,  12,  Corals;  13,  14,  15,  16, 

Plants  ;  17,  Spine  of  Echinus. 

with  Crinoids  and  a  very  simple  curled  shell  like  a  snake 
coiled  up,  a  "  Gon.atite,"  one  of  the  earliest  of  the  Ammo- 
nite class.  At  Aspen,  associated  with  the  ore-deposits  we 
found  in  the  blue  limestone  most  of  these,  together  with  a 


\ 


4« 

kind  of  snail-sholl  called  IMcnrotoTnaria.  At  I.eadville  in 
the  same  formation  Spirifcrsand  Productus arc  occasionally 
found.  A  very  curious  coral  is  one  shaped  like  a  screw, 
called  Archimedes,  after  the  author  of  the  screw.  Cup- 
corals  are  common. 

In  the  Middle  Carboniferous,  associated  with  the  coal- 
seams,  many  curious  remains  of  reeds,  ferns,  and  other 
aquatic  plants  of  that  a^c  are  found,  but  these  are  scarce 
in  Colorado  and  the  West.     The  prospector  will  observe 


Plate  XII. — Jura-tkias  Fo.ssils. 

I,  Dinosaur  Lizard  ;  2,  <,  Foot  and  Slioulder  Bone  ;  4, 4,  Vertebra  of  Sea  Sau- 
rian, Ichthyosaurus ;  5,  6, 6,  Teeth  of  Sauriansj^,  Belemnite  ;  8,  Echinus  ; 
9,  9,  Ammonites;  10,  Exogyra;  11, Trigonia  Shell. 

that  there  is  a  general  family  likeness  between  the  fossils 
of  each  division  of  the  Paleozoic  and  in  the  Paleozoic  as  a 
whole,  and  it  may  not  always  be  easy  for  him  to  determine 
whether  a  shell  is  Silurian,  Devonian,  or  Carboniferous,  but 
of  one  thing  he  will  be  certain,  that  it  is  Paleozoic. 


47 


TRIASSIC. 

In  the  Trias  thr()iiKh«>ut  the  West,  he  is  not  likely  to  find 
tnany  fossils;  the  rocks  are  generally  too  coarse;  btit  in  the 
Eastern  States,  though  he  may  not  find  any  true  remains, 
he  may  observe  the  tracks  left  by  jjreat  Saurians  as  they 
walked  on  their  hind  feet,  or  on  all  fours,  on  the  red  sands 
of  the  beaches  of  those  dreary  salt  Triassic  seas,  leaving 
"  footprints  on  the  sands  of  time"  full  of  interest. 


JURASSIC. 


In  the  Jurassic  shales  and  limestones  in  Colorad«).  he 
may  be  equally  unsuccessful,  though  in  the  upper  Jurassic 
just  below  the  Dakotah  sandstone,  he  may  light  on  the 
bones  of  gigantic  Dinosaurs,  or  great  land  lizards,  such  as 
the  author  found  in  Colorado  and  Wyoming,  monsters  sixty 
to  eighty  feet  in  length  and  proportionally  tall,  standing 
from  twenty  to  twenty-five  feet  m  height.  In  the  lower 
Jurassic  in  Wyoming,  he  will  find  great  numbers  of  sea- 
shells  and  Ammonites,  and  a  round  shell  like  a  cigar  called 
a  "  Beleninite,"  or  spear-head,  the  internal  shell  of  an  an- 
cient cuttle-fish.     Plate  XII. 


CRETACEOUS. 


In  the  Cretaceous,  beginning  with  the  lowest  group,  the 
Dakotah  group,  net-veined  leaves  of  deciduous  trees,  such 
as  the  willow,  oak,  maple,  etc.,  the  earliest  known  leaves 
of  those  kinds  of  trees,  may  be  expected  in  the  sandstone 
and  clays. 

In  the  Colorado  group  of  the  Cretaceous,  above  the  Da- 
kotah, abundance  of  oyster-shells  and  large  clam-shells 
(Inoceramus)  are  sure  to  be  found  in  the  limestones  and 
marine  shales.  In  the  Montana  group  of  the  Cretaceous 
above  this,  consisting  mainly  of  drab  shales  and  some  sand- 
stones, great  quantities  of  sea-shells  are  found,  among  them 
various  peculiar  forms  of  the  Ammonite  allied  to  the  mod- 
ern nautilus,  and  called  Scaphites,  resembling  snakes  or 


48 

worms  u.^-^  oiling,  together  with  shark's  teeth  and  bones  of 
sea  Saurian  s. 

In  the  sandstones  of  the  Laramie  Cretaceous,  remains  of 
sea- weeds  are  found ;  in  the  sandstones  immediately  below 


Plate  XIII.— Cretaceous  Fossils. 

I,  I,  Inocer^mus;  2,  Cardiuir ;  3,  Corbula;   4,  Mactra  ;  5,  Margarita ;  6,  Fascio- 

laria  ;  7,  Anehura  ;  8,  Pyrifusus  ;  0,  10,  Scaphites ;  11,  Crioceras ; 

i;<,  »>aculites  ;  13,  Shark's  Tooth. 


the  coal-beds,  and  in  those  associated  with  or  above  the 
coal,  are  found  great  varieties  of  semi-tropical  leaves,  such 
as  those  of  the  palmetto,  fig,  beech,  elm,  magnolia,  sassa- 
fras, etc.  The  presence  of  these  leaves  is  a  pretty  sure  in- 
dication of  coal. 


V 


H 


49 

TKRTIARY. 


In  the  Tertiary  Ircsh-water  beds,  siinilar  leaves  and  thm 
beds  of  poor  li^niite  coal  are  found,  together  with  fossil  in- 
sects and  remains  of  mammals.  In  the  Marine  Tertiary  are 
sea-shells. 


1 


Plate  XIV.— Tertiary  Fossils. 

,*  I'alnietlo  ;  .,  Cinnamon  Leaf  ;  3.  Cardium ;  4.  Insect ;  5,  Numiuulite 
'''•  '  Shell ;  6,  7,  Fresh- Water  Shells. 

QUATERNARY     FOSSILS. 

8.  Mammoth  lilephaufs  Tooth  ;  q,  Mastodon's  Tooth  ;  10.  Flint 
Implement  ;  II,  Stone  Grooved  by  Olacjer. 

QUATERNARY. 

In  the  Quaternary  drift,  among  the  pebbles,  sands,  and 
"  wash"  characteristic  of  gold-placer  beds,  an  occasiona 
tooth,  tusk,  or  bone  of  the  great  hairy  Mammoth  elephant 
or  the  Mastodon  elephant  may  be  discovered,  together  with 
the  stone  implements  or  bones  of  prehistonc  man  and  peb- 
bles grooved  by  glaciers. 


:.W 


so 


CHAPTER   IV. 

THE    PROSPECTORS    LITHOLOGY   OR   STUDY  OF 

ROCKS. 

A  prospector  wants  to  know  a  gredt  deal  about  rocks. 

be 

a 


They  are  his  constant  companions  in  the  field. 


o 

a 

hj 

a 

(d 

tx. 

4.1 

ol 

U 

X 

85 

H 

'o 

^ 

OQ 

f/j 

V 

t^ 

M 

u 

o 

^ 

1. 

u. 

r*'  S 

O 

>.2 

u 

to 

r ) 

t.    4-1 

55 

^§ 

•< 
< 

4i    10  . 

Scf 

a* 

£c) 

-•^ .« 

u 

"5  "3 

|5 

tn 

hH 

<«} 

P< 

r>i 

&« 

t3 

3  0 

^ 

< 

h 

u 

u 

o 

fltf 

> 

X 

X 

c 

w 

4) 

H 

E 

:1 

•5 

Ol 

Ah 

cc 

<!» 

His  busi 

I- 


I 


i 

■xf 


I 


ness  is  amongst  rocks.  1  le  wants 
to  be  able  to  recognize  them  at 
sight,  when  he  picks  up  a  loose 
pebble,  or  confronts  a  mighty 
cliff.  When  traveling  over  the 
mountains,  as  he  surveys  the 
grand  panorama  from  the  top, 
he  wants  by  the  peculiar  forms 
and  patterns  each  variety  of  rock 
is  apt  to  take  as  the  result  of 
erosion  and  weathering  owing  to 
different  degrees  of  hardness*,  to 
be  able  to  make  a  shrewd  guess 
from  a  long  distance,  as  to 
whether  one  mountain  is  made 
of  granite,  or  another  of  lime- 
stone, or  i'  third  of  porphyry. 
This  habit  of  forming  rough 
guesses  as  to  the  character  of 
distant  rocks  decides  him  as  to 
choosing  his  course  for  prospect- 
ing. "  In  those  sharp  granite- 
looking  peaks,"  he  says,  "  maybe 
1  will  find  fissure-veins.  Yonder 
cones,  like  the  spires  and  mina- 
rets of  a  Gothic  cathedral,  must 
be  porphyry  or  igneous  rock, 
another  likely  locality,  and  mark 
where  they  break  through  the 
sedimentary  strata,  and  tip  them 
up  all  around  them  ;  at  the  junc- 
tion of  these  sedimentarics  with 
the  igneous  rock  there  may  be 
limestone,  and  a  'contact  blanket 
deposit.'  Yon  smooth  grassy 
slopes  are  probably  underlaid  by 
sandstone  or  limestone,  and  the 
rolling  valley  beneath  by  soft 
shales.  The  latter  are  unprom- 
ising for  precious  ores."  Or 
again  descending  from  his  perch 
into  the  canyon  below,  he  recog- 


i'--^ 


n 
o 

3 
■o 

o 

c 


.5- 

1-1 

pi 


C/2 

> 


> 

< 

O 

r 
n 
> 

n 

> 
H 

w 
> 


o 

H 

> 
(/I 


fr 


u 


% 


./. 


■<i: 


h 


fA 


■'^.-^ 


il 


\.i^-. 


:ll' 


"^m 


5» 

nizes  the  granite  basis,  and  on  top  of  it  a  series  of  sedimentary 
rocks.   The  lowest  of  these,  by  its  rusty- white,  masonry-like 


'A 

o 

U 
< 


o 

Q 

< 
'A 

O 

u 


o 


.J 


is 
o 

U 

u 

Q 


H 

Ed 
S 

H 

s 

a. 


s 
c 
h, 

c 

0 

u 


«  a 


Sis 


5  >• 
en  >. 

u 

"0 
4)  ft, 

to 

BI   O 

3  C 
«  o 


c 
c« 

O    . 

a   ' 


Si 


structure,  he  judges  to  be  Cambrian  quartzite,  the  thin-bed- 
ded strata  above  Silurian  limestones,  and  the  heavy  massive 
beds  above  these,  Lower  Carboniferous  blue  limestone,  whilst 


53 

a  dark  greenish-gray  rock,  running  in  and  out  irrejfularly 
among  the  strata,  sometimes  between  the  stratification 
planes,  at  others  cutting  across  them,  he  judges  to  oe  an 
intrusive  sheet  of  porphyry,  and  looks  again  for  "  contact 
deposits."  A  rock  running  up  like  a  low  wall  from  the 
bottom  of  the  canyon  to  the  top  may  be  either  a  quartz 
fissure-vein  or  a  porphyry  dyke,  and  well  worth  examin- 
ing. There  are  many  ways  of  studying  rocks,  one  by  hand 
specimens,  finding  out  all  the  minerals  composing  them, 
and  then  naming  the  rocks  from  which  they  came ;  another 
by  observing  the  appearance  of  large  masses  of  rocks  in  the 
field,  and  noting  their  mode  of  occurrence ;  and  lastly,  if  wc 
wi.;h  to  be  very  accurate,  making  thin  microscopic  sections 
and  a  chemical  analysis,  but  for  the  average  prospector 
these  last  will  be  rarely  necessary. 

If  a  prospector  bought  a  manual  to  study  rocks,  for  prac- 
tical purposes,  he  would  find  himself  amongst  a  sea  of  names 
of  varieties  of  rocks,  nine-tenths  of  which  it  is  safe  to  say 
he  Avould  never  meet  with  in  his  field  experience. 

To  save  him  the  trouble  of  wading  through  such  books, 
we  select  just  about  as  much  as  a  prospector  is  liable  to 
meet  with  in  the  field  or  find  practically  useful,  saying 
little  also  about  such  common  rocks  as  are  familiar  to  every 
one. 

Those  that  need  most  definition  and  are  of  most  impor- 
tance in  the  mining-field,  are  the  crystalline  rocks  belong- 
ing to  the  class  called  metamorphic  and  igneous;  the  last 
especially  needs  careful  determination. 

Nearly  all  sedimentary  rocks  (limestone  excepted)  are 
derived  from  fragments  of  igneous  and  metamorphic  rocks. 
Probably  nine-tenths  of  the  sedimentary  rocks  are  derived 
from  granite  alone,  the  remainder  from  the  igneous  rocks, 
such  as  porphyry,  basalt,  etc.  By  describing  the  parent 
rock,  the  derivative  one  is  more  easily  made  out. 

ROCK-NJAKING    MINERALS.  ^ 


Crystalline  rocks  are  made  up  of  certain  distinct  min- 
erals, most  of  them  of  quartz,  feldspar,  and  mica,  with  some- 
times also  hornblende  and  augite.  Other  minerals  may 
locally  occur  as  occasional  elements. 

yiJART/  scarcely  needs  description,  being  kg  well  known. 


54 


The  hexagonal  prism  of  this  crystal  is  too  hard  to  be 
scratched  with  a  knife  and  will  scratch  glass.  This  distin- 
guishes it  from  calcspar  and  barite,  for  which  it  might  be 
mistaken  in  the  field;  moreover  it  will  not  effervesce  with 
acids. 

The  Feldspars  are  nearly  as  hard  as  quartz.  Their  col- 
ors are  white,  grayish,  and  flesh-color.  They  are  rarely  as 
transparent  as  quartz,  being  generally  opaque.  Their  form 
of  crystallization  is  different  from  quartz,  and  in  a  vein  they 
show  one  smooth  face  of  their  crystal,  whilst  the  quartz  is 
more  like  crushed  loaf-sugar.  In  a  porphyry  the  feldspar 
crystals  are  very  distinct,  and  give  a  characteristic  spotted 
appearance  to  the  rock.  Two  varieties  of  feldspar  are 
characteristic  of  the  crystalline  rocks,  one  called  orthoclase 
or  common  feldspar,  a  potash-feldspar,  the  other  called 
oligoclase,  a  soda-lime-feldspar.  The  former  is  very  char- 
acteristic of  granitic  rocks  as  well  as  of  igneous  porphyries; 
the  latter  is  rather  more  characteristic  of  more  recently 
erupted  igneous  rocks,  such  as  diorite,  basalt,  andesite, 
etc. 

Orthoclase  is  generally  in  large  crystals,  oligoclase  in 
small.  When  the  crystals  are  very  small,  it  may  take  a 
microscopic  examination  to  determine  to  which  variety  of 
feldspars  they  may  belong.  The  oligoclase  and  plagioclase 
crystals  in  igneous  rocks  are  commonly  but  little  white 
dots. 

To  determine  accurately,  microscopic  slides  and  chemi- 
cal tests  must  be  made,  but  this  is  scarcely  within  the  scope 
of  the  prospector  who  wants  to  guess  roughly  at  sight  as 
to  the  name  and  character  of  a  rock. 

Mica,  both  black  and  white,  needs  no  description. 

Hornblende  differs  from  mica  in  being  of  a  duller  lustre 
and  of  a  different  form  of  crystallization,  as  shown  in  the 
plate.  The  color  is  a  greenish-black;  the  greenish  tint  is 
distinct  when  the  crystal  is  struck  by  a  hammer. 

AuGiTE  or  Pyroxene  is  scarcely  distinguishable  from 
hornblende.  In  Colorado,  augite  is  mainly  confined  to  two 
kinds  of  rock,  basalt  or  dolerite  and  andesite,  both  of  com- 
paratively recent  volcanic  origin.  Hornblende  and  mica 
are  common  to  nearly  all  the  metamorphic  and  igneous 
rocks. 

Talc  amongst  miners  means  almost  any  soft,  sticky,  or 


! 


' 


ss 

slippery,  decomposed  rock,  but  strictly,  talc  is  a  pale  green 
soft  mineral  like  mica  and  is  a  silicate  of  magnesia.  Stea- 
tite or  soapstone  is  massive  talc.  Miners  often  wrongly 
call  any  soft  clay  or  rock,  soapstone  also. 

Chlorite  is  another  magnesian  mineral,  of  a  green  and 
soft  character.  Chlorite  is  again  a  name  given  to  almost 
any  greenish  rock  of  a  schistose  and  soft  decomposed  char- 
acter. 

Calcite  is  carbonate  of  lime  crystal,  the  element  of  lime- 
stone,  and  is  distinguished  by  softness  and  effervescing  in 
acids. 

Dolomite  or  carbonate  of  lime  and  magnesia  is  very  like 
calcite  and  is  the  element  of  dolomitic  or  magnesian  lime- 
stone. Dolomite  effervesces  with  much  greater  difficulty 
than  true  limestone.  To  effervesce,  the  dolomite  should 
be  powdered  and  the  acid  heated. 

GvPSUM  or  sulphate  of  lime  can  be  distinguished  by  its 
extreme  softnes  .,  being  scratched  by  the  finger-nail ;  it  does 
not  effervesce  like  lime. 

Barite  or  "  heavy  spar"  occurs  in  some  veins,  but  not  as 
a  constituent  of  rocks.  It  looks  like  calcspar,  but  is  heavier 
and  will  not  effervesce  with  acids. 

Fluor-spar  occasionally  occurs  in  veins,  in  cubes  or 
massive.  It  is  easily  scratched  with  a  knife ;  its  colors  are 
green,  purple,  yellow,  blue  or  white. 

Garnets,  Green  Epidote.  Black.  Tourmaline,  and 
other  minerals  or  gems  may  occur,  but  not  as  important 
constituents  of  the  rocks. 

crystalline  metamorphic  rocks. 

Granite. — Beginning  with  the  granitic  series  of  the  Ar- 
chaean age,  granite  proper  is  massive,  shapeless,  or  amor- 
phous, and  shows  no  bedding-planes  or  other  signs  of  for- 
mer stratification.  It  is  thoroughly  crystalline,  like  lump- 
sugar.  By  some  it  is  considered  a  true  igneous  rock,  one 
that  has  been  thoroughly  fused  by  heat,  as  much  as  the 
lavas  or  molten  iron ;  by  others  its  crystalline  amorphous 
condition  is  supposed  to  be  the  result  of  extreme  metamor- 
phism  of  originally  sedimentary  bedded  rocks,  such  as 
gneiss  or  schist,  the  two  latter  being  sometimes  traced 
down  through  a  gradual  change  into  granite.     The  compo- 


50 


sitfon  of  j^ranite  is  mica,  quartz,  and  feldspar  with  some- 
I  lines  a  little  hornblende.     The  micas  may  be  white  mica 

(muscovite)  or  black  mica 
(biotite).  Both  orthoclase  and 
oligoclase  feldspar  may  be 
present,  but  more  commonly 
the  former,  which  is  often  a 
pinkish  flesh  color.  Granite. 
in  its  crystalline  texture,  differs 
both  in  character  and  appear- 
ance from  porphyries  and  other 
igneous  rocks,  in  the  fact  that 
its  crystals  are  all  jumbled 
up  and  crushed  together  like 
loaf-sugar,  and  none  of  the 
crystals  are  set  like  plvms  in  a 
pudding,  distinctly  in  a  back- 
ing or  paste  of  very  small  crys- 
tals of  amorphous  or  glassy  ma- 
terial, as  in  the  porphyries  or 
igneous  rocks.  Granite  is  prob- 
ably the  oldest  and  deepest 
rock  known.  It  is  often  trav- 
ersed by  sparry  veins,  both 
great  and  small,  which  con- 
sist of  quartz  or  feldspar  or 
both,  in  a  more  sparry  condi- 
tion than  when  diffused  through 
the  parent  rock. 

These  so-called  "  quartz- 
veins"  are  often  called  "  granu- 
lite"  or  "  pegmatite"  or  "  graphic  granite."  The  quartz  and 
feldspar  are  often  arranged  in  parallel  plates,  giving  on 
cross-section  curious  marks  like  Hebrew  characters ;  hence 
the  word  graphic.  The  bulk  of  our  so-called  quartz  fissure 
veins  in  the  granite  mountains  may  be  called  pegmatitic 
veins.  The  colors  of  granite  vary  from  reddish  to  gray,  or 
nearly  white  to  black,  according  to  the  preponderance  and 
colors  of  the  micas  and  feldspars  in  them. 

Syenite  is  little  more  than  granite  in  which  hornblende 
supplies  the  place  of  mica. 

Gneiss    may   be    called  "bedded    granite,"  showing  a 


Plate  XVIII. 

t,  Triclinic  GligoclaseFcldsp.ir. 
7,  MDiioclinic  Orthoclase  Fekl- 
spar.  3,Carlsbad  Twins  Feldspar. 
4,  Au^ite  or  Pyroxene.  5  and 
(<,  Hornblende. 


57 

bedded  appearance.  Gneiss  is  often  cnriotislv  and  pret- 
tily banded  r.  streaked  by  seams  of  mica  dovetailing  into 
each  other.  If  mica  preponderates,  it  is  called  "mica- 
gneiss,"  if  hornblende  "  hornblendic  gneiss." 

Schist  may  be  called  laminated  gneiss  or  granite,  being 
finally  divided  into  lamina  or  leaves.     This  foliated  struc- 


Gkanitc 

Platk  XIX. 


I'l.ATK    XX. 


SvcMtrc 
Pf.ATK    XXI. 


ture  is  due  to  the  arrangement  of  the  flat-lyin^^  crystals  of 
mica  or  hornblende  largely  composing-  it.  It  may  be  a 
mica-schist  or  a  hornblende-schist. 

Slatk  is  shale  altered  by  heat  into  a  hard  crystalline 
structure. 

QUARTZITE  was  Originally  a  sandstone  composed  of 
quartz-grains,  which  by  heat  have  been  partially  fused  to- 


.,»w*»>5H!>»: 


&NtlSS 

Plate  XXII. 


C0WT0flTCflM»C/(5cHiST 

Plate  XXIII. 


Plate  X\I\. 


gather  at  the  edges,  resembling  granules  of  tapioca  in  a 
tapioca  pudding.  Quartzite  differs  from  quartz  in  being 
a  rock  made  out  of  pieces  of  quartz,  and  not  the  original 
mineral  itself.  Quartzite  may  be  white  like  sugar,  gray, 
brown,  or  rusty.     It  shows  a  true  stratified  structure. 

Marisle  is  limestone  similarly  changed  to  a  more  crystal- 
line condition. 


58 

Serpentine  is  a  gn'een  magnesian  rock,  sometimes  found 
with  marble  and  igneous  rocks,  and  is  formed  by  alteration 
of  certain  minerals  in  the  latter. 


CRYSTALLINE   I(;NE()1:S   OR   ERUPTIVE   ROCKS. 

• 

These  are  rocks  which  are  supposed  to  have  been  thor- 
oughly fused  or  melted  in  the  bowels  of  the  earth.  Some 
reach  the  surface  by  fissures  or  volcanic  vents,  others  have 
never  attained  to  the  surface  or  overflown  it,  but  have  in- 
truded themselves  between  the  weak  places  in  the  underly- 
ing strata,  or  have  collected  and  cooled  deep  down  below 
the  surface  in  great  molten  reservoirs  called  "  laccolites" 
or  lakes  of  stone.  When  these  have  been  subsequently  un- 
covered by  erosion,  they  may  present  the  forms  of  consid- 
erable mountain  masses  like  the  Elk  Mountains,  and  Henry 
Mountains  and  Spanish  Peaks.  Geologists  distinguish 
those  rocks  which  have  poured  out  on  the  surface  from 
craters  and  volcanic  vents  as  volcanic  rocks,  while  those 
cooling  below  are  called  Plutonic. 

INTRUSIVE   PLUTONIC   ROCKS. 

The  component  minerals  of  these  intrusive  Plutonic 
rocks,  such  as  are  commonly  called  porphyries,  are  prin- 
cipally quartz  and  feldspar,  with  mica  or  hornblende.  In 
color  these  rocks  are  some  shade  of  gray,  green,  or  maroon, 
or  even  white,  but  their  most  striking  characteristic  is  a 
general  spotted  appearance.  This  arises  from  more  or  less 
large,  distinct,  perfectly  formed  crystals  of  feldspar  or 
quartz,  set  in  a  finer-grained  crystalline  paste  or  back- 
ground, standing  out  distinctly  from  it.  This  base  or  back- 
ground may  be  comparatively  coarsely  crystalline,  finely 
crystalline,  or  so  finely  crystalline  that  the  crystals  can  be 
discovered  only  by  a  microscope,  while  the  larger  crystals 
seem  set  in  the  paste,  like  plums  in  a  pudding.  In  the 
depths  of  a  mine  the  porphyry  is  commonly  much  decom- 
posed by  water  action  or  mineral  solutions,  and  even  passes 
into  a  clay  or  gouge.  The  characteristic  spotty  appear- 
ance, from  the  presence  of  individual  crystals  of  feldspar, 
may  even  then  identify  the  rock,  or  by  chemical  analysis 
the  very  aluminous  character  of  the  decomposed  rock  may 


59 

determine  its  character.  When  feldspar  is  the  main  con- 
stituent, it  is  called  a  felsite  porphyry,  when  a  certain 
amount  of  quartz  is  present  a  quartz  porphyry. 

DiORiTE,  whose  crystals  are  sometimes  porphyritic  in 
character,  hence  called  porphyritic  diorite  or  porphyrite, 
belongs  also  to  this  intrusive  or  Plutonian  class,  differing 
only  from  the  others  in  the  fact  that  its  feldspar  is  of  the 
triclinic  plagioclase  kind  rather  than  orthoclase.  Horn- 
blende is  a  prominent  constituent  of  this  rock,  and  gives  it, 
more  or  less,  its  dark  olive-green  tint.  In  appearance  it 
resembles  a  dark  syenite,  but  its  occurrence  as  an  eruptive, 
intrusive  rock  distinguishes  it.  as  syenite  is  generally  a 
metamorphic  rock.  The  peaks  of  the  Elk  Mountains  are. 
many  of  them,  of  diorite.  Diorite  or  porphyrite  is  the 
so-called  porphyry  of  Aspen,  above  the  ore  deposits. 


PeiVHYmTicniomTs 
Plate  XXV. 


gUART/    HORPHVRIES. 

These  are  the  commonest,  and  may  be  said  to  be  the  pre- 
vailing eruptive  rocks  associated  with  our 
ore  deposits  in  Colorado,  as  for  instance  at 
Leadville,  felsite  porphyries  as  well  as 
quartz  porphyries  occur  in  the  granite  rocks 
in  the  Central  and  Georgetown  mining 
districts.  All  these  rocks  are  common 
through  the  West,  and  quartz  porphyries 
are  the  most  common  eruptive  rocks  the 
prospector  is  likely  to  meet  with  in  his 
search  for  ore  deposits.      We  will  describe 

in  detail  one  or  two  typical  species,  though  it  must  be  ob- 
served that  these  porphyries  are  of  endless  varieties  and 

shades  of  appearance. 
Quartz    porphyry. — A  quartz  porphyry 

is  a  porphyry  that  contains  quartz  crystals 

large  or  small,  in  addition  usually  to  large 

orthoclase  feldspar  crystals,  generally  of  a 

vitreous    glassy   variety   called  "  sanidin," 

together  with  small  crystals  of  hornblende 

or  mica.     As    a  typical  example  we   take 

that  which  forms  the  dyke  composing  the 

peak  of  Mt.  Lincoln.  Colorado,  called  Mt. 

Lincoln  quartz  porphyry.      This  porphyry 


riLSITtPOHfMYRY 

Plate  XXVL 


Plate  XXVII. 


and  varieties  of  it  are  comtnon   in   the   western   mining; 

sections  of  Colorado. 

In  appearance  it  is  a  Rray  rock  spotted 

with  large  and   small   crystals  of  ortho- 

clase  sanidin  feldspar,    which     sometimes 

show  an  oblong  face  two  inches  long,  by 

an  inch  wide ;  at  other  times  a  shape  like 

the  gable-end   of  a  house,    according  to 

whichever    part   of   the   crystal    happens 

to   be  exposed.    Sometimes  two  crystals 

are  seen  locked  together,  forming  what  are 

called  Carlsbad  twins.     When  the  rock  is 

decomposed,  these  crystals  not  unfrequently  drop  out  and 

lie  as  pebl)les  on  the  ground.    With  these  may  be  also  seen 

rounded  ends  of  bluish  crystals  like  broken  glass.     These 

are  portions  of  perfect  quartz  cry.stals, 
which  when  extracted  show  a  six-sided 
pyramid  at  either  end.  These  larger 
crystals  are  set  in  a  crystalline  ground 
mass  of  much  smaller  crystals  of  the 
same  kind,  together  with  many  little 
black  cubes  of  shining  mica,  or  duller 
lustred,  longer,  rectangular,  oblong  crys- 
tals of  hornblende.  This  porphyry  is 
eruptive    and    intrusive,   occurring    in 

dykes,  intrusive  sheets  and  laccolites. 

Lkadvillk  White  Porphyry. —At  Leadville  there  is  a 

quartz  porphyry  known  as  the  Leadville  white  porphyry  or 

"  block  porphyry"  by  the  miners,  which  needs  description, 

as  it  is  the  one  that  more  especially  is 

asso(  iated  with  the  rich   ore  deposits. 

It  is  a  white,  compact,    homogeneous 

looking  rock,  not  unlike  a  shaly  white 

sandstone  or  quartzite.     It  consists  of 

feldspar,  quartz  and  a  little  mica.    Its 

porphyritic  or  spotted  character  is  so 

indistinct  that  one  would  be  inclined 

to  call  it  a  felsite  at  sight  rather  than 

a  true   porphyry,  but  the  microscope 

reveals  perfect  double  pyramids  of  quartz  and  individual 

crystals  of  feldspar  set  in  a  paste  of  the  same  minerals. 

It    is    often    stainiul    by    concentric   rings    of   iron  oxide 


I'l.A'.'E    XXVIII. 


HoHMBitNotAuureJ^iO^s 

MMNCTITC&ARNtr. 

Plate  XXIX. 


6i 

nnd  marked  with  \vondcrfiil  imitation^  of  tree?*.  The 
latter  have  earned  for  it  the  title  of  "  photo^jrapliit- 
roek"  or  "dendritic  porphyry."  These  tnarkitigs  are 
only  the  crystallization  forms  of  oxide  of  irtm  or  man- 
ganese, something  like  fern-frost  on  a  window-pane. 
The  porphyry  is  very  shaly,  and  breaks  up  in  thin  slabs; 
hence  called  also  "  block  porphyry."  It  is  common  at  Lead- 
villc  and  is  also  found  elsewhere.  In  the  same  rejjion  there 
are  many  other  varieties  of  quartz  porphyry  such  as  the 
"gray  porphyry."  the  Sacramento,  and  the  pyritiferous 
porpyhry.     The  latter  is  often  gold  bearing. 


V<)rN<;KK    KKKIJSIVK    VOft  ANIC    ROCKS. 

These  intrusive  plutonic  porphyries  and  diorites  arc  gen- 
erally older  than  the  other  class,  which  reached  the  stirfai  e 
and  poured  over  it  and  which  may  be  called  for  distinction 
"  effusive"  volcanic  rocks. 

Typical  of  these  we  may  cite  the  dark  basalts  and  doler- 
ites  that  often  cap  the  table  lands  of  the  prairie  region  and 
overlie  our  coal  beds.  A  pinkish  or  dove-colored  rhyolile 
also  caps  some  of  the  mesas  and  in  certain  districts  an 
andesite  lava. 

DoLERiTE  AND  Basalt. — The  la^  2r  being  scarcely  more 
than  a  fine-grained  variety  of  the  former, 
are  very  dark  rocks,  consisting  of  dark, 
heavy  minerals,  such  as  augite,  magnetite, 
and  a  plagioclase  feldspar  called  labradorite. 
Such  minerals  are  said  to  be  basic,  and  the 
rock  composing  them  also  basic. 

Andesite  is  very  like  dolerite,  though 
generally  a  lighter  gray  or  pink.  Both 
augite  and  hornblende  may  occur  in  it, 
more  especially  hornblende,  sometimes  mica 
also.  The  feldspar  is  called  andesite  feldspar  from  the 
Andes  Mountains. 

Rhvolite,  under  the  microscope,  shows  a  peculiar  flow- 
ing structure,  hence  its  name  from  " rheo'  to  flow.  The 
lighter  rocks  in  Colorado  and  the  West  are  generally  rhyo- 
lites  rather  than  true  trachytes.  Their  colors  are  pale 
gray,  white,  pink,  or  sometimes  dark. 

Rhyolite  consists  of  a  fluent,  vitreous,  ground  mass  or 


Plate  XXX. 


63 

paste,  usually  containing  crystals  of  sanidin  feldspar,  or 
even  of  quartz.  When  these  crystals  are  conspicuous  so  as 
to  give  the  rock  a  porphyritic  appearance  it  is  called 
"liparite." 

In  some  cases  it  may  have  even  a  granite-like  ap^^ear- 
anre,  the  crystals  of  quartz,  mica  and  feldspi^r  being  more 
or  less  intermixed;  then  it  is  called  Nevadite.  It  is  an 
acidic  rock  consisting  of  acid  minerals  mainly. 

Trachyte,  from  *  trachus"  rough,  is  alight  colored  rock, 
with  a  peculiar  characteristic  rough  feel,  due  to  micro- 
scopic vesicularity.  It  consists  of  a  ground  mass  '  sani- 
din feldspar  and  augite,  containing  crystals  of  the  '.atter. 
In  ninety-nine  cases  out  of  a  hundred,  in  Colorado  at  lea^i, 
also  in  the  West,  rocks  which  are  popularly  called  "  tra- 
chytes" are  rhyolites  or  porphyries. 


Awv»OAtO/OAL  Scon/A 
I'LATE    XXXI. 


AnocsiticBkcddi^ 
Plate  XXXII. 


Basalts  and  some  of  the  other  extrusive  volcanic  rocks 
assume  a  columnar  form  on  cooling.  Also,  on  the  surface 
of  the  flow,  the  lava  becomes  minutely  honey-combed  like 
sponge,  from  escape  of  steam.  This  is  called  scoria,  and 
wiien  these  holes  are  filled  with  almond-shaped  white  crys- 
tals, amygdaloid.  At  other  times  the  rock  is  a  volcanic 
breccia;  that  is,  angular  blocks  of  lava,  great  or  small,  are 
cemented  together  by  lava.  This  probably  was  caused 
when  the  lava  was  pouring  out  of  the  fissure  s^lowly,  some 
portions  congealed  and  were  broken  up  by  the  onward 
flow,  and  again  involved  in  the  molten  mass  vvi+hout  being 
remelted.  Enormous  masses  of  volcanic  breccia  cover  the 
San  Juan  region.  Sometimes,  by  steam,  the  lava  is  blown 
into  dust  and  descending  with  water,  is  worked  up  into  a 
volcanic  sandstone  known  as  volcanic  "  tafa"  or  '  tuff." 

Obsidian  is  vitrified  lava  or  volcanic  glass. 


6;> 


CHAPTER   V. 
THE    PROSPECTOR'S    MINERALOGY. 

There  are  two  classes  of  minerals  in  which  the  prospector 
is  interested,  one  may  be  called  the  "  earthy"  minerals,  such 
as  quartz,  calcspar,  etc.,  associated  with  the  precious  ores; 
the  other,  the  metallic  minerals,  constituting  the  ores  them- 
selves. 

Both  of  these  he  wants  to  know  at  sight,  or  to  determine 
with  the  simplest  appliances.  (Generally  speaking,  his 
eyesight,  his  pocket-knife,  his  ore-glass  and  a  little  acid 
will  be  all  he  needs,  nor  need  he  concern  himself  about  a 
great  number  of  minerals,  if  he  only  knows  the  commoner 
ones  well.  The  earthy  minerals  form  the  gangue  or  vein- 
stone of  the  vein  in  which  the  precious  ores  are  distributed. 


c 
e 
d 
e 
d 

g 
e 

n 

a 


EARTHY   OANGUE   MINERALS. 

These  are  principally  quartz,  calcite,  or  limespar,  dolo- 
mite, fluorspar  and  baryta,  all  of  which  we  have  already 
described  among  rock-forming  minerals.  These  crystals 
are  nearly  always  to  be  found  in  the  adjacent  rock  as  ele- 
ments of  that  rock,  and  their  more  sparry  condition  in  the 
gangue  of  the  vein  is  derived  by  solution  from  the  enclos- 
ing country  rock.  Thus,  a  vein  running  through  granite 
will  contain  mainly  quartz,  though  calcite  and  fluorspar 
may  be  associated  with  it  in  small  quantities.  A  vein 
passing  through  limestone  naturally  carries  calcite  or  lime- 
spar.  Sometimes  baryta  is  associated  with  the  calcite,  es- 
pecially if  near  the  limestone  ore  deposit  there  are  porphy- 
ries. 

Baryta  has  been  detected  as  an  element  of  some  porphy- 
ries which  are  probably  ore-bearing,  and  when  prospecting, 
we  have  found  baryta  to  be  generally  an  indication  of  ore 
near  by,  while  calcspar,  or  quartz,  alone,  may  or  may  not 
be  barren.  The  float,  or  loose  surface  indications  of  ore 
deposits  at  Aspen  is  commonly  made  up  of  calcspar  and 
baryta. 

Fluorspar  in  Colorado  is  generally  confined  to  veins  in 


.•■  ■•-tjt-nuMtia.ar  iSi  liMMW-^ 


an 


the  granitic  rocks  and  in  some  of  the  eruptive  rocks.     Its 
presence  is  a  good  sign  of  ore. 

(.>xiDKS()h  Iron  and  Manganf.sk. — These,  often  mixed  to- 
gether, form  a  large  element  in  the  gangue  matter  of  a 
vein  or  ore  deposit.  Manganese  can  be  recognized  by  its 
dark  black  color.     A  beautiful   rose-colored  carbonate   of 

manganese  called  Rhodocrositf, 
is  occasionally  met  with,  associ- 
ated with  quartz  and  metal  in 
some  veins. 

Carbona  TK  (ti  C(>Pi»KR  IS  often 
associated  with  this  gangue 
matter.  It  is  readily  distin- 
guished by  its  bright  green  or 
azure  blue  color.  "  Float"  is 
commonly  rusty  with  iron  oxide 
streaked  vith  stains  of  copper 
carbonate. 

Spathic  Iron  or  Iron  Car- 
honate  or  Siderite  occurs  here 
and  there  in  the  gangue  of  fissure  veins.  It  is  very 
like  brown  feldspar,  but  heavier.  These  few  common  min- 
erals cover  nearly  all  that  are  generally  met  with  as  indi- 
cations of,  or  in  important  connection  with,  ore  deposits. 

As  a  rule,  most  of  these  minerals  occur  in  a  massive  state 
rather  than  as  individual  crystals  in  a  vein. 


I'l.ATE    XXX  ill. 
Spathic  Iron, 


METALLIFEROUS    MINERALS. 


Through  these  gaflgues  of  vafiotis  ctiaraicteis,  t1>*»  pre- 
cious metals  are  distributed  in  long,  narrow  patches  or 
strings,  or  in  large  crystalline  massjes,  or  in  scattered  crys- 
tals, or  in  decomposed  masses.  The  gangue  matt«:-r  is  gen- 
erally in  the  majority  in  a  vein,  ar^d  the  ore  thinly,  spar- 
ingly, and  irregularly  distributed  in  it.  When  a  vein  is 
said  to  be  ten  or  more  feet  wide,  it  is  not  to  be  supposed 
that  ten  feet  of  solid  ore  is  meant,  but  that  mis  is  the  width 
of  the  gangue  between  walls.  The  ore  bod^'  nnsay  be  only 
a  few  inches  wide.  The  streak  or  marn  body  of  <i;Te,  called 
the  "  pay  streak,"  has  a  tendeno >-  to  kt  f  >  near  one  wall  or 
the  other,  or  at  times  to  cross  from  wali  ,o  wall. 


EEifl 


<55 


HIGH    AND    LOW    (.KAr^F.   ORES. 


Plate  XXXIV. 

Ruby  Silver. 


In  gold  veins,  flakes  or  wires  of  "  free"  or  "  native"  gold 
occur  in  the  decomposed  gangue.  and  sometimes  in  the 
pure,  undecomposed  quartz :  "  native" 
silver  is  found  in  much  the  same  way, 
but  more  as  specimens  than  as  continuous 
bodies.  Isolated  patches  of  rare  or  valu- 
able minerals,  such  as  Ruby  silver,  Horn 
silver.  Silver  glance,  etc.,  occur  locally 
in  parts  of  the  vein,  sometimes  coating 
stalactites  or  crystals  of  a  "  vugh"  or 
cavity  lined  with  qaartz  or  other  crystals. 
An  assay  from  such  picked  specimens 
would  give  a  very  unfair  average  of  a  mine  or  prospect. 

The  bulk  of  the  profits  of  a  mine  come  from  the  com- 
moner minerals,  such  as  galena,  pyrite,  or  lead-carbonate, 
and  from  the  average  grade  of  the  mine.  In  California 
gold  mines,  the  average  yield  of  gold  per  ton  is  $i6.  In 
Dakota,  $6.  In  the  silver-lead  mines  of  Leadville,  $40  per 
ton  is  the  average,  and  the  ores  are  mostly  low  grade.  A 
few  miles  of  extraordinary  high  grade  may  yield  from  $75 
to  $100  per  fon,  but  these  are  exceptional.  Quantity  of 
ore,  facility  tor  milling,  co^t  of  freight,  the  size  of  the 
vein,  and  iti:  facility  for  working  and  nearness  to  market 
give  the  offset. 

DECOMPOSFD    MINERALS. 


ir 


1- 
r- 
is 
d 
:h 

y 

d 
)r 


Sometimes  the  gangue  matter  contains  a  variety  of  de- 
composed ore  in  rich  secondary  combination  intimately 
mixed  through  its  mass  and  rarely  discernible  by  the  eye. 
Thus,  yellow  mud  from  a  mine  may  assay  high,  from  the 
presence  of  invisible  chlorides  or  sulphurets  of  silver.  No 
accurate  estimate  of  the  value  of  a  mine,  or  even  of  a  piece 
of,  ore,  can  be  found  without  an  assay  or  mill -run.  The 
reason  for  such  richness  in  decomposed  surface  products 
is,  that  nature  has  been  for  ages  leaching  out,  concentrat- 
ing, and  combining  in  richer  forms  the  essence,  so  to  speak, 
of  the  vein. 

Gray  Copper  (Tetrahedrite).— Besides  the  ordinary 
galena  and  pyrites  common  in  most  mines,  we  sometimes 

S 


66 


find  considerable  bodies  of  gray  copper  in  mines,  or  inter- 
mingled with  other  ores.  This  is  genr»-ally  a  rich  silver- 
bearing  ore,  running  from  sixty  ounces  to  some  thousands 
per  ton.     It  generally  occurs  massive,  rarely  showing  its 

pyramidal  "  tetrahedrite"  crystals. 
In  appearance  it  is  not  unlike  a 
freshly  broken  piece  of  bronze.  It 
is  more  common  in  fissure  veins  in 
granite  and  eruptive  rocks  than  in 
limestone.  In  Halls  Valley,  Color- 
ado, it  is  associated  with  baryta  in  a 
vein  in  the  gneiss.  It  occurs  in 
the  Georgetown  veins  in  granite. 
In  the  San  Juan  district  it  occurs  also 
associated  with  baryta  in  the  Bonanza 
,^  .    ^  ,  ,,  ^  mine ;  and  an  ore  not  identical  with 

Gray  Copper  (Tetrahedrite.)  ..  .  -j.-         *     ^  ^•■^       'j.   • 

'     *^'  It  in  composition,  but  very  like  it  in 

appearance,  called  bismuthinite,  consisting  of  bismuth,  an- 
timony, copper  and  silver,  is  characteristic  of  that  region 
and  is  rich  in  silver.  Bismuthinite  has  a  more  shiny,  tin- 
like appearance  than  gray  copper,  and  the  red  color  which 
bismuth  gives  to  charcoal  under  the  blowpipe  readily  dis- 
tinguishes it  from  gray  copper. 


Plate  XXXV. 


LOCAL   VARIATIONS   IN   VALUE  OF  ORES. 


There  are  locally  in  different  mining  districts  consider- 
able differences  in  the  value  of  certain  minerals  and  ores. 
In  one  district  g^ray  copper  may  rarely  exceed  sixty  ounces 
of  silver;  in  another  it  is  invariably  over  one  hundred 
ounces. 

A  coarse  galena  is  generally  poor  in  silver,  while  fine 
grained  "  steel  galena"  is  generally  rich  in  silver,  but  the 
reverse  may  also  be  the  case.  In  some  of  the  mines  at 
Aspen,  fine-grained  galena,  especially  near  the  surface,  is 
quite  poor  in  silver,  while  in  other  mines  in  the  same  dis- 
trict it  is  exceedingly  rich.  Localities  occur  also  where 
coarse-grained  galena  runs  well  in  silver  and  is  richer  than 
fine-grained  galena.  This  is  the  case  at  the  Colonel  Sel- 
lers mine  at  Leadville.  So  one  mining  district  or  even 
one  mine  is  not  a  rule  for  another. 

Pyrites. — Iron  pyrites  and  copper  pyrites,  common  in 


67 


most  of  our  quartz  veins  in  granite  and  in  the  eruptive 
rocks,  may  yield  both  gold  and  silver,  but  usually  the  for- 
mer. There  are  certain  districts  more  characterized  by 
pyrites  than  others,  such  as  the  Central  City  district. 
The.se  are  generally  gold-producing  districts  Some  of  the 
mines  at  Breckenridge  and  South  Park  have  strong  pyri- 
tiferous  veins  in  eruptive  dykes,  such  as  the  Jumbo  mine. 
These  have  of  late  produced  a  great  deal  of  gold.  The 
same  district,  however,  produces  large  argentiferous  lead- 
veins.  Pyrites  generally  favors  the  granite,  eruptive  and 
crystallized  rocks.  The  quartzites  of  the  Lower  Silurian 
of  South  Park  and  Red  Cliff  are  often  pyritiferous  and  gen- 
erally gold-bearing.  In  limestone  the  pyrites  is  rare  or 
absent,  its  place  being  filled  by  some  form  of  iron  oxide. 
In  the  deeper  mines  of  Leadville,  however,  this  iron  oxide 
is  beginning  to  pass  down  into  the  iron  sulphide  or  pyrite 
from  which  it  was  derived.  Iron  pyrites  can  generally  be 
distinguished  from  copper  pyrites  by  its  paler,  more  brassy 
color,  by  its  superior  hardness,  and  by  its  crystallizing  in 
cubes.  Copper  pyrites  is  much  yellower  and  softer,  and 
crystallizes  in  a  more  pyramidal  form.  A  vein  may  glit- 
ter with  showy  pyrites  and  yet  be  quite  valueless.  It  usu- 
ally yields  more  gold  in  its  decomposed,  oxidized  condition 
than  in  its  unaltered  state.  In  the  one  case  the  gold  is 
free-milling,  and  in  the  other  it  must  be  smelted  at  much 
greater  expense. 

SuLPHURETS. — This  tei-m  among  miners  is  loosely  used, 
and  often  means  some  decomposed  ore  whose  ingredients 
cannot  be  determined  at  sight,  but  which  somehow  assays 
high  in  silver.  True  sulphuret  or  sulphide  of  .^ilver 
is  a  name  embracing  a  large  family  of  rich  silver  ores, 
among  which  are  stephanite  or  brittle  silver,  argentite 
or  silver-glance,  sylvanite  or  graphic  tellurium,  and 
polybasite. 

All  these  rich  ores  are  compounds  of  sulphur  and  silver 
and  other  ingredients  in  varying  proportions.  They  are 
somewhat  alike  in  appearance  and  not  always  so  easy  to 
distinguish. 

Argentite,  silver  glance,  or  sulphuret  of  silver,  is  of  a 
blackish,  lead-gray  color,  easily  cut  with  a  knife,  and  con- 
sists of  an  aggregate  of  minute  crystals.  Its  composition 
in  loo  parts  is  sulphur  12.9,  silver  '7.1.     Under  the  blow- 


68 


pipe  it  gives  of¥  an  odor  of  sulphur  and  yields  a  globule  of 
silver. 

Stephanite,  or  "  brittle"  or  "  black" 
silver,  is  closely  allied  to  argentite.  Its 
composition  is  sulphur,  antimony,  and 
silver,  silver  being  68.5  per  cent.  The 
crystals  are  small.  Under  the  blow-pipe 
it  gives  oft  garlic  fumes  of  antimony 
and  yields  a  dark  globule  from  which,  by 
adding  soda,  we  get  pure  silver. 

PoLYBASiTE,  commou  at  Georgetown 
and  in  some  of  the  Aspen  mines,  such  as 
the  Regent  or  J.  C.  Johnson,  on  Smuggler 
Hill,  is  like  the  others,  but  of  a  more  flaky, 
scaly  and  graphitic  appearance.  It  is 
not  unlike  very  fine-grained  galena, 
yielding   150  to  400  ounces  of  silver  per  ton. 

These  sulphurets  sometimes  line  little  cavities  in  lime- 
stones with  a  dark  sooty  substance,  which  under  the  micro- 
scope proves  to  be  crystals  of  one  of  the  sulphurets  of 
silver.  Sometimes  also  a  rock  is  stained  all  through  a 
blackish  gray  by  these  sulphurets.  Iron  or  manganese 
may  produce  much  the  same  effect,  but  an  assay  will  soon 
reveal  the  difference.  Associated  with  such  a  rock  we  may 
see  flakes  or  wires  of  native  silver,  that  have  emerged  from 
the  sulphide  state. 


Plate  XXXVI. 

Stephunite. 


^  1 


CHLORIDES. 


Chloride  of  Silver  ("  Horn  silver,"  or  Cerargyrite). — 
This  is  another  result  of  secondary  decomposition  from  a 
sulphide  state  (slver  sulphide).  It  is  a  greenish  or  yellow- 
ish mineral,  like  wax,  and  easily  cut  with  a  knife.  It  is  a 
very  rich  ore,  running  75.3  per  cent,  silver,  the  remainder 
being  chlorine.  As  a  secondary  product  of  decomposition 
it  is  generally  found  near  the  surface  or  in  cavities,  some- 
times deposited  on  calcite  or  other  crystals.  In  the  mines 
at  Leadville  it  is  commonly  associated  with  other  decom- 
posed ores,  such  as  carbonates.  In  the  Chrysolite  mine,  a 
mass  weighing  several  hundred  pounds  was  found.  Chlo- 
ride, bromide,  and  iodide  of  silver  are  closely  related,  being 
compounds  of  chlorine,  bromine,  iodine  and  silver.     It  is 


69 

noticeable  that  these  salts  are  the  elements  of  sea  water, 
and  that  these  ores  are  often  found  in  marine  limestones. 
According  to  Mr.  Emmons,  the  change  at  Leadville  from 
sulphide  to  chloride  was  produced  by  surface  waters;  these 
waters  are  found  to  contain  chlorine,  which  they  probably 
derived  from  passing  through  the  dolomitic  limestones 
which  contain  chlorine  in  their  crystals,  and  these  lime- 
stones perhaps  originally  derived  it  from  the  sea  water  in 
which  they  were  deposited.  Chloride  of  silver  is  found  at 
Aspen  and  abundantly  in  the  outcrop  of  mines  in  New  and 
Old  Mexico. 

SULPHARSFNITKS. 

Ruby  Silver  (Pyrargyrite  and  Proustite). — Composed  of 
sulphur  17.7,  antimony  22.5,  silver  5q.8=ioo.  Crystallizes 
in  rhombohedrons,  is  seen  in  spots  or  crystals  on  a  mass  of 
ore  of  a  deep  red  or  blackish  tint.  When  scratched  with  a 
knife  it  shows  a  bright  or  deep  red  color.  In  some  mines 
this  very  rich  ore  occurs  only  as  specimens,  but  in  others  it 
is  present  in  sufficent  quantity  to  largely  influence  the 
value  of  the  ore  in  bulk.  In  parts  of  the  Granite  Mountain 
Mine  in  Montana,  it  constitutes  the  principal  ore,  associ- 
ated, however,  with  other  minerals.  It  there  occurs  in 
large  masses  and  accounts  for  the  extraordinary  richness  of 
that  celebrated  mine.  Proustite  is  much  the  same,  only 
lighter  red,  and  consists  of  sulphur  19.4,  arsenic  15.1,  silver 
65.5  =  100. 

CARBONATES. 


This  term  also  embraces  a  large  family,  the  commonest 
being  carbonate  of  lead  (cerussite)  and  carbonate  of  cop- 
per (malachite  and  azurite). 

Copper  Carbonate  can  never  be  mistaken,  owing  to  its 
brilliant  green  and  azure  blue  color.  Copper  stains  are 
among  the  common  surface  signs  of  a  "  lead."  It  is  gener- 
ally associated  also  with  rusty  stains.  Both  are  the  surface 
products  from  copper  and  iron  pyrites  forming  a  vein  below 
ground  which  may  or  may  not  be  profitable.  Copper  stains 
are  common  enough  in  many  rocks,  but  do  not  always  lead 
to  bodies  of  ore.    In  South  Park  the  red  Triassic  sandstones 


70 


are  so  stained,  but  yield  no  ore.  Along  our  foothills  there 
is  quite  a  stained  belt  from  Golden  to  Morrison  and  through 
Bergen  Park.  But  few  promising  deposits  of  copper  or 
other  ores  have  been  found,  although  handsome  specimens 
of  native  copper  have  been  discovered  near  Golden. 

At  the  Malachite  Mine  on  Bear  Creek,  near  Morrison,  a 
prospect  was  at  one  time  opened  showing  a  good  deal  of 
silicate  of  copper  (chrysocolla)  and  malachite,  but  for  some 
reason  it  has  not  been  worked  since. 

CoiM'ER  in  its  native  or  uncombined  state  is  rare  in  Col- 
orado, and  so  far  we  have  &s  yet  no  true  profitable  mine. 
A  great  deal  of  copper  is  found  associated  with  other  ores, 
and  is  extracted  by  some  of  the  smelters.  Carbonate  of 
copper  is  commonest  in  the  limestone  districts,  as  might 
be  expected  from  the  carbonating  influence  of  limestone 
upon  minerals  in  it,  or  mineral  solutions  passing  through  it. 
Carbonate  of  iron  (spathic  iron,  or  siderite)  constitutes 
part  of  the  gangue  matter  in  some  of  our  veins,  and  may 
also  be  found  associated  with  coal  seams  generally,  in  the 
latter  case  in  an  oxidized  condition. 

Cerussite  (Carbonate  of  lead). — This  is  mostly  found  in 
the  limestone  districts,  such  as  Leadville.  It  is  there  known 
in  two  forms,  one  called  "hard  carbonates,"  the  other 
"soft"  or  "sand  carbonates."  The  crystals  of  this  ore  are 
small  prisms,  sometimes  combined  into  a  cross  shape,  of  a 
pale  grayish  white,  and  might  be  taken  for  some  form  of 
carbonate  of  lime  or  gypsum ;  their  weight,  however,  soon 
shows  the  difference.  They  are  a  secondary  product  of 
decomposition,  consisting  of  carbon  dioxide  and  lead  oxide ; 
as  a  carbonate  they  effervesce  in  nitric  acid,  and  yield  lead 
when  heated.  Cerussite  is  exceedingly  rich  in  lead,  carry- 
ing seventy-five  per  cent.  The  white  lead  of  commerce 
has  the  same  composition.  In  Leadville  and  elsewhere  in 
Colorado  it  is  silver-bearing  also,  and,  though  low  in  silver, 
the  facility  of  its  treatment  at  the  smelter  makes  it  a  very 
desirable  ore.  As  a  rule  it  contains  less  silver  than  the  un- 
altered galena,  but  is  more  easily  treated  than  the  latter. 
The  process  of  change  or  derivation  from  a  sulphide  state 
{i.e.,  from  galena)  to  a  carbonate,  is  well  shown  sometimes 
in  a  piece  of  Leadville  ore.  A  central  cube  of  galena  is 
surrounded  by  a  grayish  green  ring  of  sulphide  of  lead  or 
anglesite.  and  outside  this  may  again  occur  crystals  of  lead 


11^ 


7» 

carbonate.  Thus  the  process  is  from  a  sulphide  to  a  sul- 
phate, then  to  a  carbonate.  The  so-called  "  hard  carbo- 
nates" is  a  brown  mass  consisting  of  a  hard  flinty  combina- 
tion of  iron  oxide  and  silica,  impregnated  with  crystals  of 
lead  carbonate,  with  which  are  often  silver  chlorides,  also. 
The  "  sand  carbonates"  result  from  the  decomposition  and 


Plate  XXXVII. 

Simple  and  Compound  Crystals  of  Carbonate  ot  Lead  (Cerussite). 

breaking  up  of  the  hard  carbonates,  or  from  a  mass  of  pure 
crystals  of  carbonate  of  lead,  which  are,  by  nature,  loose 
and  incoherent.  The  Leadville  mines  are  getting  below 
these  products  of  decomposition  and  entering  upon  the 
original  sulphides  of  galena  and  iron.  The  yield,  how- 
ever, is  said  to  be  equally  good. 

ZiNC-BLENDE  (SPHALERITE)    "BLACK   JACK"). — Common    in 

most  mines  mixed  with  other  ores.  As  it  is  a  very  refrac- 
tory mineral  in  smelting,  much  of  it  is  not  desirable  in  a 
mine.  It  is  easily  recognized  by  its 
brown  resinous  look,  or  when  very  black 
by  its  pearly  lustre.  At  Georgetown, 
near  the  surface,  brown  "rosin-zinc- 
blende"  carries  silver,  and  is  associated 
with  rich  ores,  such  as  polybasite  and 
gray  copper.  With  depth  the  zinc- 
blende  becomes  more  abundant  and 
blacker,  and  loses  much  of  its  silver 
properties.  Zinc-blende  may  run  from 
nothing  to  twenty  dollars  silver,  and  rarely  as  high  as  $ioo 
per  ton. 

In  some  mines  in  the  San  Juan  it  occurs  abundantly  near 
the  surface  and  fades  out  with  depth.  We  have  no  true 
zinc  mines  in  Colorado,  the  zinc  being  mixed  with  other 
ores.     In  some  mines  in  Pitkin  County  the  zinc  predomi- 


Plate  XXXVIII. 

Zinc  Sulphide  (Zinc 
Blende). 


72 

nates  over  all  other  ores,  and  though  it  runs  high  in  silver 
the  smelters  do  not  care  to  take  it,  on  account  of  its  refrac- 
tory character.  In  the  Eastern  States  where  zinc  smelting 
is  a  specialty,  such  ore  might  be  separated  and  both  silver 
and  zinc  saved.  In  Missouri  zinc  and  lead  are  found  to- 
gether. 

In  Colorado  there  are  no  mines  of  one  mineral  alone,  as 
in  some  other  parts  of  the  world.  We  have  no  true  lead, 
zinc  or  cr,p^)er  mines;  these  baser  metals  are  either  argen- 
tiferous or  auriferous,  and  their  baser  qualities  are  sacri- 
ficed for  their  richer  ones. 


CHAPTER   VI. 
ORE    DEPOSITS. 


i 


THEORIES    REGARDINO     IHK    ORIGIN    OF    ORE-DEPOSITS. 

A  prospector  will  find  both  a  practical  as  well  as  scien- 
tific interest  in  considering  the  origin  of  ore  deposits. 
Where  do  the  precious  metals  come  from?  What  is  their 
origin?  How  are  mineral  veins  formed  and  how  do  pre- 
cious metals  get  into  them? 

The  remote  origin  of  metals  is  a  matter  of  speculation. 
They  may  have  formed  part  of  that  gaseous  mist  from 
which,  according  to  the  nebular  theory,  our  planetary  sys- 
tem was  evolved.  As  this  passed  into  molten  condition 
the  metallic  vapors  may  have  separated  into  various  com- 
binations, and  consolidated  and  been  arranged  in  the  gen- 
eral make-up  of  the  world  according  to  their  specific 
gravity.  Some  have  thought  that  the  interior  of  the  earth 
may  be  more  metalliferous  than  the  surface  crust,  since  the 
earth  grows  heavier  toward  the  centre.  Volcanic  rocks 
coming  up  from  depths  unknown  contain  a  large  per  cent, 
of  the  heavier  metals,  particularly  iron.  But  we  turn  from 
these  speculations  to  theories  of  more  practical  interest  to 
the  prospector. 

A  prevalent  theory  among  miners  and  prospectors  is 
what  may  be  called  "  the  igneous  theory"  or  the  fiery  origin 
of  veins  and  metals.  They  are  apt  to  attribute  the  fissures 
themselves  to  some  violent  volcanic  outburst,  and  consider 


7J 


the  quartz  g:anf!nic  or  veinstone,  together  with  the  metalH. 
as  molten  volcanic  emanations,  filling  at  one  tin)e  a  wide, 
gapin>f  fissure. 

Others  demand  an  intense  heat,  considering  that  the  met- 
als in  the  veins  were  reduced  in  the  bowels  of  the  earth  by 
intense  heat  to  a  vaporous  condition,  which,  ascending 
through  the  fissures,  condensed  and  consolidated  in  a  crys- 
talline form  in  the  upper  and  cooler  portions  of  the  fissures, 
as  certain  sublimed  mineral  vapors  from  a  smelting  furnace 
sometimes  collect  and  recrystallize  in  the  flues. 

By  many  prospectors  every  indication  or  surface  appear- 
ance of  a  vein,  or  even  a  likely-looking  rock,  is  called  "  a 
blow  out,"  a  term  suggestive,  at  least,  of  some  sort  of  vol- 
canic explosion  at  that  point.  With  them,  the  "  fire  and 
brimstone"  origin  of  ore 
deposits  is  as  deep  seat- 
ed as  the  veins  in  the 
rocks. 

These  ideas  contain  a 
measure  of  truth,  and 
were  naturally  suggest- 
ed by  observing  that  our 
ore  deposits  are  so  gen- 
erally associated  with 
volcanic  rocks  and  evi- 
dences of  past  heat ;  and 
it  cannot  be  denied  but 
that  the  presence  of 
these  volcanic  rocks  had 
more  or  less  to  do  with 
the  ore  deposits. 

The  modern  study  of 
ore  deposits  inclines  to 
the  belief  that  we  need 
not  draw  directly  upon  the  unknown  profound  supposed 
ignited  regio.is  of  the  earth's  interior  for  the  direct 
source  of  metals  found  in  the  veins,  nor  entirely  from 
violent  explosive  volcanic  agencies,  nor  from  very  intense 
heat,  but  racher  that  we  may  look  nearer  home  for  the  im- 
mediate source  of  both  metals  and  veinstone,  namely,  in 
the  elements  of  the  common  country  rock  adjacent  to  the 
ore  deposits;  and  for  the  medium  of  distribution  and  con- 


•     *    ♦     •    ♦      \*  *  ♦ 

Plate  XXXIX. 


*♦  *♦* 


Fold  Passing  into  Fault  Showing:  Broken 
Character  of  Fault  Fissure  and  Adjacent 
Rocks  Producinff  Later  a  Brecciated 
Vein  and  "  Horses." 


14 


centration  of  ore  nnd  veinstone  from  nothing  more  violent 
or  volcanic  than  wattT,  more  or  less  heated  and  alkaline. 
Nor  is  it  so  absolutely  necessary  to  suppose  that  the  filling 
of  a  vein  fissure  with  quartz  or  metal  must  needs  come  up 
from  profound  depths,  and  from  a  foreign  source ;  but  quite 
as  likely  from  the  adjacent  sides  of  the  fissure,  or  even  from 
above  the  position  later  occupied  by  ore. 

Veins  of  whatever  kind  are  not  vents  for  molten  volcanic 
matter,  but  simply  courses  for  water,  more  or  less  heated 


Plate  XL. 

A  Tight  Fault  Crevice  Ueingr  At- 
tacked by  Solutions  ProducitiK 
Finally  a  Narrow  Fissure  Vein- 
Small  Dots  =  Ore  Solutions. 


Plate  XLI. 

GnHh  Vein  FiHsures  in  Jointed  Rrup* 
tive  Sheet. 


and  alkaline,  in  fact,  channels  of  mineral  hot  springs  carry- 
ing earthy  minerals  and  metals  in  the  same  solution,  and 
depositing  them,  partly  by  cooling  and  sometimes  by  chem- 
ical precipitation  and  mainly  by  relief  of  pressure  in  such 
openings  or  weak  places  as  may  be  found  convenient. 

The  origin  of  these  openings  and  weak  places  in  the 
earth's  crust  is  various.  The  class  of  great  fissures  hold- 
ing "  fissure  veins,"  cleaving  our  mountains  from  top  to 
bottom  to  an  unknown  great  depth,  were  caused  by  the 
fracturing  and  faulting  of  rocks,  in  the  gradual  process  of 
folding  upward,  and  elevation  of  the  mountain  system,  a 
process  so  slow  and  gradual  that  it  may  be  even  progress- 
ing now  without  one  noticing  it.  The  relief  of  extreme 
tension  from  folding  results  finally  in  faulting ;  though  the 
fault  fissure  may  extend  to  very  great  depths,  it  was  prob- 
ably not  violent  but  gradual.     From  tmie  to  time,  the 


75 

Hhock  produced  by  the  g:rindinjf  tojfctitLT  of  the  walls  of  a 
tissurc,  in  a  slip  or  jerk  of  only  a  few  inches,  may  have 
given  rise  to  severe  earthquakes  on  the  surface. 

A  great  fault  fissure,  too,  was  likely  to  be  accompanied 
by  minor  adjacent  faults,  and  also  by  small  incipient  fis- 
sures or  loose  fractures  of  the  rocks,  producing  parallel 
fissures  and  zones  of  fissure  veins.     Other  openings,  occu- 


-*-^s*^-^^ 


:\ 


h 


^f 


Plate  XLIl. 

Joints  and  Bedding  Planes. 


>''^  ^ 


Plate  XLIII. 

Jointed  Granite. 


pied  now  by  fissure  veins,  may  be  compared  to  those  joints 
common  to  all  rocks,  the  result  of  contraction  and  shrink- 
''ge  of  the  granitic  or  volcanic  rocks  from  a  soft,  semi- 
plastic  condition  to  one  more  solid  and  compact.  But  in 
no  case,  we  think,  were  the  fissures  now  occupied  by 
veins  50  to  100  feet  wide  originally  wide  open  chasms 

like  that  which  swallowed  up  Korah, 
Dathan  and  Abiram  in  Bible  history, 
but  rather  cracks  fitting  very  tightly 
together  by  enormous  lateral  pressure, 
such  as  we  see  in  fault  cracks  of  the 
present  day,  not  yet  occupied  by  vein- 
stone or  gangue  or  metal  matter. 
These  narrow  cracks  were  worked  up- 
on by  alkaline  and  acid  solutions  and 
enlarged  'jy  the  process,  the  rock  gradually  eaten  into  being 
replaced  by  gangue  and  metal  matter,  a  process  often  fur- 
ther assisted  by  the  shattered  character  of  the  rock  comm  >n- 
ly  found  adjacent  to  a  great  fault :  this  shattered  cavity  was 
sooner  or  later  eaten  out,  so  to  speak,  and  replaced  by  min« 


Plate  XLIV. 

Jointed  Slate. 


eral  matter.  Some  of  the  broken  rock,  being  not  consumed 
in  this  way,  was  left,  forming  fragments  in  the  vein,  which 
when  small  are  called  "  breccia'"  and  when  large  "horses." 
The  gfreat  "  gash"  fissures,  such  as  we  find  occuped  by  so- 
called  fissure  veins  in  volcanic  sheets  such  as  those  of  the 
San  Juan  region,  Colorado,  appear  to  be  due  hot  so  much 
to  great  earth  movements,  like  the  last,  as  to  openings 
formed  by  cooling  and  contraction  of  the  lava,  somewhat 
as  may  be  obset-ved  on  the  cooling  of  iron  in  a  slag  fur- 
nace.    Ore  deposits  of  lead  and  other  ir.'nerals  forming 


/  / 


ManltttSi 


Plate  XLV. 

Joints  in  Columnar  Basalt. 


Plate  XLVI. 

Contact  Ore  Deposits  Between  Porphyry 
and  Limestone. 


beUvied  deposits  in  limestones  find  their  way  in  solution 
through  the  vertical  joints  common  to  all  water-formed 
rocks,  resulting  from  contraction  in  consolidating  from  a 
soft,  muddy  condition.  Such  fissures  are  short,  but  they 
act  as  channels  to  a  more  important  line  of  weakness  occu- 
pied by  the  main  body  of  the  blanket  ore  deposits,  viz., 
the  dividing  line  between  one  stratum  and  another.  An- 
other line  of  weakness  for  the  attack  of  mineral  solutions 
is  at  the  juncture  of  a  porphyry  sheet  or  dyke  with  some 
other  rock.  The  interval  between  them  is  often  occupied 
by  a  "  contact  vein."  The  heat  of  the  volcanic  matter  to- 
gether with  steam  may  have  influenced  the  solutions,  even 
if  the  porphyry  did  not  actually  supply  the  metallic  ele- 
ment in  t'le  vein. 


KOI  i>iN«    ANH  kai:i,tin«;. 

In  the  many  and  xreat  -ipheavals  of  the  earth's  crust,  re- 
siiltinjif  in  conlinents  risinj:^  above  tlie  sea,  and  on  those 
continents  still  greater  and  sh»r]>er  upheavals  forming 
mountain  ranges,  rocks  hav»*  l>een  nuch  broKcn  and  frac- 
tured, from  great  fractures,  i--^  lang  fissures  miles  in  length 
and  depth,  down  to  little  crack-s  of  but  a  few  inches.  Much 
of  this  fracturing  has  been  caused  by  the  folding  and 
crumpling  upward  of  strata  into  mour.tains.  accompanied 
by  great  crushing  and  mashing  togeth  'r  of  the  rocks. 
When  this  lateral  tangential  folding  and  compression  of  the 
rucks  reaches  its  maxfmum  int*;nsity,  the  rocks  break,  and 
a  fault  or  slip  is  the  result,  with  its  attendant  fault-fissure. 
This  relieves  the  strain  for  a  wV'  .  but  the  shock,  doubt- 
less at  the  time  accompanied  by  arth  quakes  on  the  sur- 
face, resulted  in  a  general  breaking  up  of  the  adjacent 
country  into  many  parallel  and  smaller  faults  and  cross 
faults,  besides  a  gene-al  shattering  of  the  ground  inter- 
mediate to  the  faults.  A  region  thus  faulted  and  shattered 
is  Justin  the  desired  condition  for  forming  a  future  mineral 
belt  or  mining  region,  when  the  cracks  and  scars  thus  made 
have  been  healed  and  filled  up  by  mineral  matter,  brought 
in  through  the  agency  of  watery  solutions  more  or  less  al- 
kaline or  heated. 


A 


INTRUSIVE    KiNKOUS    ROCKS. 

When  these  fault-fissures  descend  to  a  very  great  depth, 
taey  may  tap  the  molten  rock  reservoir  supposed  to  lie  be- 
neath great  mountain  ranges,  and  the  molten  lava  or  por- 
phyry rushes  upward  through  the  weak  line  of  the  fissure, 
fills  it  with  its  matter,  which  on  cooling  becomes  a  dyke 
instead  of  a  mineral  vein.  These  eruptive  rocks  may  or 
may  not  reach  quite  to  the  surface  and  overflow  it  in  a  lava 
sheet.  Tf  they  do  not,  they  find  relief  by  intn^ding  them- 
selves laterally  between  the  layers  of  stratified  vocks,  whose 
leaves  or  bedding  planes  may  have  been  partially  opened, 
like  the  leaves  of  a  crumpled  book  by  previous  action  of 
folding.  In  such  cases  the  porphyry  dyke  or  intrusive 
sheet  may,  if  it  be  mineralized,  answer  all  intents  and  pur- 
pose of  a  mineral  vein,  or  the  ore  may  be  found  on  one  or 
both  sides  of  such  a  sheet,  in  the  line  of  separation  and 


78 


weakness  between  it  and  the  adjacent  strata,  or  it  may 
permeate  and  mineralize  by  a  "  substitution"  process  an  ad- 
jacent porous  or  soluble  rock,  such  as  limestone.  Thus  both 
in  the  dyke  or  intrusive  sheet  itself,  as  well  as  at  its  contact 
with  other  rocks,  the  prospector  should  look  for  signs  of 
precious  metal. 

If  the  dyke  or  sheet  should  be  decomposed,  clayey,  and 
rusty,  it  may  contain  free  gold  disseminated  through  i'., 
which,  at  a  depth  which  may  or  may  not  be  ever  reached 
by  mining,  passes  into  the  auriferous  iron-pyrites  from 
which  the  free  gold  originally  came.  In  this  case  the  ore 
will  be  no  longer  "  free"  or  "  free-milling,"  but  of  a  charac- 
ter that  must  be  subjected  to  the  more  expensive  treatment 
of  roasting  or  smelting.  Little  stringers  or  veinlets  of 
quartz,  if  observed  in  such  an  eruptive  rock,  should  he  care- 
fully examined  as  the  most  likely  source  of  the  richest  gold 
ore.  Some  of  our  most  noted  gold  mines  in  the  West  are 
in  these  "  rotten"  mineralized  dyk.s  or  eruptive  intrusive 
sheets.  "  Likely  signs"  in  such  would  be  rusty  "  gossan" 
stains  of  green  carbonate  of  copper  and  gouge  or  clay  mat- 
ter. It  is  worth  obsf.'rving  that  the  dyk  j  may  be  only  valu- 
able as  a  mine  as  far  down  as  the  decomposition  lasts  and 
as  long  as  the  ore  continues  in  a  free  state.  With  depth, 
the  pyrites  of  the  undecomposed  lower  portion  of  the  dyke 
may  be  found  too  poor  in  gold  to  pay  for  smelting  even. 

As  this  desirable  state  of  decomposition  is  the  result 
mainly  of  the  action  of  surface  waters,  a  prospector  may 
consider  sometimes,  where,  on  the  outcrop  of  such  a  dyke, 
the  rock  is  most  likely  to  be  deepest  aJected  by  surface  ac- 
tion ;  for  example,  more  probably  below  the  old  stream  bed 
than  on  the  top  of  a  mountain,  but  this  is  not  always  the 
case.  Most  dykes  and  intrusive  sheets  when  mineralized 
are  mineralized  by  pyrites  rather  than  by  galena;  hence 
they  are  generally  more  gold-bearing  than  silver-bearing. 
The  contact  deposits  adjacent  to  a  volcanic  rock  may  have 
been  aided  in  their  deposition  by  steam  issuing  from  the 
molten  mass,  or  by  heated  waters  or  steam  ascending  with 
it,  or  generally  by  the  heat  of  the  dyke,  as  heat  together 
with  moisture  is  a  great  solvent  of  rocks  and  promoter  of 
chemical  action. 

In  granitic  rocks,  if  a  "  contact"  deposit  occurs  adjacent  to 
a  porphyry  dyke,  it  is  usually  a  quartz  vein,  or  a  vein  com- 


79 


posed  of  quartz  and  feldspar,  commonly  called  "  pegmatite." 
Such  contact  fissure  veins  may  be  on  one  or  both  sides  of  a 
dykie.  The  telluride  veins  of  Boulder  and  the  gold  and 
silver  veins  of  Idaho  Springs.  Central  and  (leorgetown  in 
Colorado  are  often  so  situated. 


CONTACT   DEPOSITS. 


When  a  porphyry  sheet  intrudes  itself  into  limestone  as 
at  Leadville,  the  ore  may  be  looked  for  on  either  side  of 


ContaetOrit 


CoiOactOTe 


OreBea 


Contact  Ore'i 


Gnei4s 


^     Gneiss 


Plate  XLVII. 

•'  Contact  Blanket  "  Ore  Deposits  and  "Contact  Fissure  Veins." 

this  sheet;  but  more  commonly  below  it.     At  first  the  ore 
seems  to  permeate  the  limestone  immediately  at  the  line 


^m^mmmmmmmm 


of  contact,  but  from  this  somewhat  horizontal  line  it  is 
apt  to  run  down  through  joint  cracks  in  the  limestone,  en- 
larging the  cracks  by  solution,  and  substituting  or  replac- 
ing the  dissolved  rock  with  silver-lead  ore,  by  a  process 
called  "  metasomatic  substitution." 

"  Metasomatic"  means  literally  "an  interchange  between 
one  body  and  another."  In  this  case  it  is  an  interchange 
between  metal  and  limestone,  by  which  the  limestone  is 
gradually  replaced,  molecule  by  molecule,  with  metallic 
matter.  Thus  we  may  suppose,  that  as  the  mineral  solu- 
tions were  working  on  the  limestone,  rotting  and  soaking 
and  dissolving  it,  as  each  molecule  of  lime  was  dissolved 
it  was  replaced  or  substituted  by  a  molecule  of  metallic 
matter,  until  a  large  body  of  the  rock  was  replaced  by  ore. 
This  appears  to  be  the  true  way  in  which  most  of  our  ore 
bodies  were  formed  in  limestone  and  other  soluble  rock, 
rather  than  that  they  were  "  washed  in"  and  "  deposited"  in 
"  pre-existing  large  cavities"  as  some  have  supposed. 

BI,ANKET   DEPOSITS   ON    BEDDING   PLANES. 

The  solutions,  having  worked  their  way  down  through 
these  vertical  joints,  may  reach  a  second  line  of  weakness, 
viz.,  the  bedding  plane  or  line  of  stratification  between  one 
bed  or  stratum  of  rock  and  another,  and  deposit  along  it  as 
on  a  floor.  This  may  be  between  one  heavy  bed  of  lime'- 
stone  and  anothei.  If  it  is  between  two  dissimila?-  rocks, 
such  as  between  limestone  and  quartzite,  or  even  between 
limestone  and  magnesian  limestone  called  dolomite,  it 
comes  under  the  name  of  a  "  contact"  deposit.  Thus  it  is 
noticeable  that  besides  great  fissures,  lines  of  weakness  or 
"  bedding  planes"  are  favorite  places  for  ore  deposits,  to 
which  the  natural  vertical  joints  often  act  as  feeders,  as 
well  as  themselves  containing  large  "  pockets"  or  "  cham- 
bers" of  ore.  When  the  deposits  are  confined  to  these 
"  pockets"  and  there  appears  to  be  no  "  blanket"  deposit, 
the  mine  is  said  to  be  "  pockety,  "  and  after  a  "  pocket"  is 
exhausted  an  immense  amount  of  money  and  work  and 
blind  "  gophering"  often  follows  in  hunting  for  another 
pocket.  There  is  in  this  case  little  rule  to  guide  the  pros- 
pector. Locally,  by  experience  in  the  mine,  he  may  notice 
that  some  fine  line  of  gypsum,  calcspar,  or  iron  stain  is  apt 
to  lead  to  a  pocket  and  follow  it.     In  the  mines  of  Aspen, 


ftl 


where  the  mineral  zone  lies  irregularl)'  but  generally  near 
about  the  line  where  the  limestone  becomes  dolomized.  a 
miner,  when  his  ore  "  plays  out,"  follows  as  closely  as  he 
can  this  line,  which  he  is  able  to  do  by  the  different  hard- 
ness of  the  limestone  and  dolomite,  the  latter  causing  his 
f)ick  to  "ring."  In  every  mine  there  is  generally  some 
ocal  sign  to  assist  the  miner  in  following  up  his  lost  ore. 

SURKACK    SIC;NS. 

The  prospector  in  hunting  on  the  surface  oiitcrop  for 
signs  of  such  contact  or  blanket  or  pocket  deposits  must 
look  out  for  signs  of  decomposition  along  the  line  of  con- 


OreZon0 


Ore 


Plate  XLVIII. 

Prospecting  with  Diamond  Drills. 

tact,  such  as  lead  carbonates,  carbonate  of  copper,  oxide  of 
iron,  together  with  crystalline  matter,  such  as  calcspar, 
Q;ypsum,  or  baryta.     He  may  also  observe,  in  the  vertical 


8a 

joints  leadinj?  down  from  the  surface  into  the  body  of  the 
limestone,  rusty  clay  fillings  and    iron  stains,     in  these 

"blanket"  bedded  deposits, 
prospects  on  a  large  scale  may 
sometimes  advantageously  be 
made  by  drilling  with  diamond 
drills  from  the  surface  down 
through  as  many  of  the  strata 
as  are  suspected  of  being  ore 
bearing ;  the  "  cores"  brought 
up  will  show  if  an  ore  body  has 
been  penetrated,  together  with 
its  approximate  thickness  at  a 
certain  point,  and  if  this  process 
is  continued  over  a  certain 
area,  the  approximate  areal 
lin-'it  of  the  ore'body  may  be  as- 
certained. This  work  may  fol- 
low upon  a  clo^  e  examination 
first  of  mineral  signs  along  the  outcrop,  it  is  sometimes 
done  after  an  area  has  been  exploited  foi  some  time  by 


Plate  XLIX. 

Brecciated  Lode  with  Quartz 
Geodes. 


Plate  L. 

Bzecciated  Vein. 

actual  mining  with  a  view  of  discovering  new  bodies  or 
cojr.tinuations  of  the  ore. 


TRUE   FISSURE  VEINS. 


Whilst  profound  fault  cracks  may  be  filled  by  lava,  those 
not  descendhig  to  such  great  depths  doubtless  lay  open, 
till  they  were  gradually  filled  by  solutions  carrying  in 
earthy  vein-stone  and  metallic  matter ;  in  a  word  they  were 


83 

the  channels  of  mineral  or  hot  springs.  It  must  not  be 
supposed  that  these  fault  cracks  were  ever  "  open  chasms" 
commensurate  in  width  with  the  wide  dykes  and  veins  now 
found  in  them,  but  rather  in  some  cases  very  close-fitting 
cracks,  mere  lines  of  weakness,  the  walls  appressed  closely 
together  by  prodigious  lateral  pressure.  In  other  cases  the 
fissure  would  be  rather  a  shattered  zone  passing  down 
through  the  strata,  than  one  definite  line  of  fissure.  Doubt- 
less when  the  molten  lava  ascended  through  these  fissures 
it  greatly  widened  them  to  admit  of  its  volume.  In  the 
case  of  true  fissure  veins,  the  fissure  or  shattered  zone  was 
enlarged  by  the  corroding,  substituting  power  of  acid  min- 
eral solutions  till  we  have  to-day  a  fissure  vein  twenty  to 
fifty  or  more  feet  in  width.  In  the  shattered  zone,  this 
substituting  process  would  go  on  easily  and  rapidly,  until 
nearly  all  the  shattered  fragments  were  replaced  by  min- 
eral matter  except  a  few  "  indigestible"  pieces,  which,  if 
small,  would  cause  what  is  called  a  brecciated  vein,  and  if 
large,  "  horses"  in  a  vein.  These  fragments  are  not  so 
much  pieces  that  have  fallen  from  above  into  an  open  fis- 
sure gradually  filling  up  with  solutions  of  quartz  and  vein 
m.atter  in  which  they  became  entangled,  but  rather  undi- 
gested, unsubstituted  fragments  of  the  wall  rock,  imme- 
diately adjacent  to  the  fragments,  for  at  times  some  line  in 
the  fragment  corresponds  to  a  line  in  the  adjacent  wall- 
rock  without  evidence  of  any  serious  displacement.  Again, 
the  shadowy  outlines  of  fragments  can  be  observed  par- 
tially but  not  entirely  replaced  by  quartz  or  vein  matter. 
Sometimes  the  "  breccias"  are  surrounded  by  rings  of 
quartz  or  metal,  and  called  "  cockade  ores." 


HORSES. 

In  the  San  Juan  region  in  Colorado,  where  we  have  won- 
derful opportunities  of  observing  extensive  sections  of 
great  fissure  veins  descending  the  faces  of  cliffs  on  either 
side  of  a  canyon  for  two  or  three  thousand  feet,  such  broad 
veins  at  intervals  split  up  into  two  or  three  arms  enclosing 
large  fragments  or  "  horses '  of  the  lava  country  rock,  and 
again  unite  to  form  the  main  vein.  These  veins  occupy  a 
once  shattered  fissure,  the  walls  of  which  were  originally 
neither  straight  nor  regular,  but  shattered  and  cracked. 


«4 

The  vein  matter  insinuated  itself  between  the  shattered 
portions,  sometimes  forming  a  "  breccia"  of  small  frag- 
ments, at  others  "  >•  rses"  of  Targe  ones. 

The  appearance  of  these  great  San  Juan  veins  from  a 

little  distance  is  that  of  broad 
yellow  stains  of  oxide  of  iron 
contrasted  with  the  sombre  gray 
of  the  1  a va  rocks.  In  some  places 
in  this  region  the  quartz,  by  rea- 
son of  its  superior  hardness, 
stands  up  above  the  softer  lava 
like  a  low,  rusty,  or  white  wall. 
Again,  at  other  localities  instead 
of  being  a  bold  outcrops  the  vein 
is  represented  by  a  sharp,  shal- 
low depression  forming  a  nar- 
row little  ravine  or  trench,  the 
path  of  a  rivulet  and  zone  of 
abundant  vegetation.  In  this 
case  the  vein  was  full  of  decom- 
posable minerals,  such  as  pyrite, 
whose  oxidation  decomposition 
products  were  washed  out  leav- 
mg  a  depression  in  the  rocks. 

So,  amongst  some  of  the  indications  of  a  fissure  vein  to 
the  prospector  we  may  note  : 

I  St.  Brown  or  green  stains  on  rocks. 

2d.  A  bold  quartz  vein  like  a  wall  above  the  country. 

3d.  A  narrow  ravine  or  gulch. 

4th.  The  path  of  a  rivulet  and  exuberant  growth  of  vege- 
tation. 

SIGNS    OF    FAULTING. 

As  these  fissure  veins  are  generally  the  filling  of  fault 
cracks,  and  the  fissures  are  mainly  due  to  faultio.g,  a  pros- 
pector should  be  able  to  recognize  the  surface  and  other 
signs  of  faulting. 

Faulting,  as  we  have  said,  is  generally  the  result  of  ex- 
treme folding.  So,  in  entering  a  mountain  region  by  way 
perhaps  of  a  canyon  cutting  right  through  it  on  the  exposed 
face  of  the  cliffs,  he  may  observe  some  of  these  folds  or 
arches,  low  and  gentle  at  first,  but  gradually,  as  the  range 


Plate  LI. 

Horse  or  Rider. 


n 


is  penetrated  further,  increasing  in  sharpness,  steepness, 
and  closeness;  with  this  increase  we  may  CA^ect  faults. 
The  presence  of  the  fault  may  be  indicated  by  a  little 
"  sag"  or  depression  in  the  outline  of  the  hill,  or  by  a  line 
of  rubbish  and  broken  rock  descending  the  face  of  the  cliff, 
or  by  a  zone  of  exuberant  vegetation,  or  by  the  pathway  of 
a  little  rivulet.  He  will  observe  a  general  fractured  ten- 
dency of  the  rocks  as  they  approach  the  fault  line.  By 
closer  search  he  may  notice  pieces  of  rock  polished  or 
slickensided  by  the  movement  of  the  walls  of  the  fault 
slipping  and  grinding  upon  one  another.  Slickenside  is  a 
sure  proof  of  motion  having  taken  place  in  the  rocks,  and  is 
often  observed  on  the  walls  of  fissure  veins.  A  much 
faulted  region  is  often  marked  by  a  step-like  outline,  each 
step  representing  the  fallen  or  risen  side  of  a  fault  block. 
These  fault-lines  should  be  carefully  examined  for  mineral 
indications,  especially  if  the 
fault  line  is  occupied  by  a 
porphyry  dyke  or  a  vein  of 
quartz  or  calcspar.  Some- 
times these  fault  lines  arc 
totally  barren,  both  of 
quartz,  veinstone,  or  metal- 
liferous matter.  Tho>  may 
be  filled  up  with  clay,  rub- 
bish, and  broken  roi.k,  or 
the  two  walls  may  be  ac- 
tually welded  tojfether  by  pressure  accompanied  by  a  cer- 
tain amount  of  heat,  producing  local  metamorphio  action. 

Faultiiit,  tuo  in  some  regions  may  have  occurred  com- 
paratively recently,  or  at  least  after  the  period  u.ost 
marked  by  deposit  of  mineral  solutions  and  ore  deposits, 
in  which  case  the  fissures  may  be  barren  or  at  present  oc- 
cupied by  hot  or  mineral  spimgs  making  veins  for  the 
future.  A  stupendous,  cofnparattvely  modern  fault  runs 
along  the  west  base  of  the  Wahsatch  Mountains  in  Utah; 
its  line  is  marked  by  a  series  <  I  hot  springs. 

Along  the  face  of  a  canyon  wall  the  piospector  may  no- 
tice some  peculiar  stratum  tiear  the  top  of  the  cliff  and  its 
counterpart  out  of  pliMse  ne»r  the  bottom,  showing  that  a 
fault  has  occurred,  whose  aJMount  of  slip  he  can  easily  esti- 
mate or  measure;  but  when  a  fault  of  many  thousands  of 


if=^^^^ 


Plate  LI  I. 

Vein  a  Faulted  by  Cross-Vein  B. 


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86 


feet  occurs,  a  knowledge  of 
the  different  geological  peri- 
ods involved  in  the  slip  is  nec- 
essary to  estimate  the  amount 
of  fall.     Thus,  if  a  prospector 
by  his  geological  knowledge 
should  recognize  a  Cretaceous 
rock,  brought  up  in  close  jux- 
taposition to  a  Silurian  rock, 
he  would  know  that  a  stupend- 
o    ous  fault  had  occurred  at  that 
^    place,   involving    the    entire 
^  thickness  of  the  rocks  compos- 
^  ing  the    periods  intervening 
j2    between  the  Silurian  and  the 
o    Cretaceous. 

■5  That  a  faulted  region  is  one 
f  in  which  great  folding  due  to 
S  lateral  tangential  pressure  has 
o  taken  place,  the  folds  eventu- 
u  ally  breaking  dov/n  in  faults, 
t  is  well  seen  in  the  structure 
E  of  the  Mosquito  Range  in 
^  South  Park,  Colorado,  which 
2  embraces  the  Leadville  min- 
■5    ing  district. 

fa       The  comparatively  horizon- 
's   tal  strata  of  the  Park  as  they 
*    approach  the  Mosquito  Range 
.§   begin    to    fold     gently,    the 
o    folds  gradually  increasing  in 
steepness    and    closeness    as 
they  approach  the  axis  of  the 
range.     As  we  pass  up  Four 
Mile  Canyon,  which  shows  a 
complete  cross  section  of  the 
range,  we  find  the  axis  to  be 
formed  by  a  magnificent  and 
very  steep  arch,  well  shown  on 
the  face  of  Sheep  Mountain, 
which, having  arrived  at  its  ut- 
most tension,  breaks  down  in 


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what  is  called  the  London  mine  fault,  traversing?  and  split- 
tin>c  the  ran^c  for  twenty  miles.  The  line  of  the  fault  is 
shown  by  a  depression  between  Sheep  and  Lamb  Moun- 
tains. In  nearly  every  canyon  along  the  flank  of  this  range, 
the  line  of  the  fault  is  easily  traced  by  similar  arches  and 
"  sags,"  and  by  a  peculiar  wavy  look  of  the  turfed  strata  as 
they  bend  down  toward  the  fault.  As  we  penetrate  further 
across  the  range,  we  pass  a  series  of  such  faults,  each  one 
formerly  represented  by  a  steep  fold  that  preceded  the 
faulting.  Hence  it  is  that  we  descend  from  the  top  of  this 
range  down  into  Leadville  and  the  Arkansas  Valley  by  a 
series  of  gigantic  steps  or  benches,  each  bench  represent- 
ing a  fallen  faulted  block.  Faults  have  their  points  of 
maximum  depth  and  disturbance,  from  which  they  are  apt 
to  die  out  at  either  end  in  folds  or  rounded  hills.  Great 
faults  are  accompanied  by  minor  parallel  and  cross  faults. 
The  ultimate  cause  of  this  folding  and  faulting  is  attrib- 
uted by  some  geologists  to  the  interior  of  the  earth  grow- 
ing colder  and  contracting,  causing  the  surface  crust  to 
shrink  and  fold  in  adapting  itself  to  the  shrinking  interior. 
Prof.  J.  F.  Kemp  says:  "The  strains  induced  by  cooling 
and  contraction  of  the  earth  are  the  most  important  cause 
of  fracture.  The  contraction  develops  a  tangential  strain, 
which  is  resisted  by  the  arch-like  disposition  of  the  crust. 
Where  there  is  insufficient  support,  gravity  causes  a  sag- 
ging of  the  material  into  troughs  or  synclinal  folds  which 
leave  corresponding  arches  or  anticlinal  folds  between 
them.  Where  the  tangential  strain  is  greater  than  the 
ability  of  the  rocks  to  resist,  they  are  upset  and  crumpled 
i  *o  folds  from  the  thrust.  Both  kinds  of  folds  are  fruitful 
cv.w.»esof  fissuring  cracks  and  general  shattering,  and  every 
slip  from  yielding  sends  its  oscillations  abroad,  which 
cause  breaks  along  all  lines  of  weakness." 


JOINTS. 

Joints,  common  to  all  rocks,  appear  to  be  due  not  so 
much  to  faulting  and  motion,  as  to  shrinkage  of  the  rocks 
in  passing  from  a  soft  matter  or  muddy  condition  to  one  of 
consolidation.  A  good  many  so-called  fissure  veins,  even 
in  the  granite  series,  appear  to  occupy  extensive  joint 
cracks,  rather  than  fault  planes.     These  may  be  due  to  the 


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WEBSTER, N.Y.  I45S0 

(716)  S72-4903 


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general  shrinkage  of  the  whole  mountain  mass  in  consoli- 
dating from  a  semi-plastic  or  aqueo-i^eous  state  of  soften- 
ing to  one  more  consolidated  and  rigid. 

The  joints  in  lava  sheets  forming  curious  columns,  like 
those  of  the  Palisades  of  the  Hudson,  are  due  to  the  same 
shrinkage  from  a  molten  state.  Such  joints  may  sometimes 
be  mineralized  for  a  short  depth,  forming  what  are  called 
"gash"  veins,  rather  than  true  fissure  veins.  The  joints 
in  sedimentary  rocks  are  due  to  consolidation  from  a  soft, 
muddy,  incoherent  condition ;  such  joints  may  similarly  be 
occupied  by  gash  veins,  or  may  lead  to  pockets  or  wide 
blanket  deposits. 

The  line  of  weakness  between  one  stratum  or  one  set  of 
strata  and  another,  often  a  favorite  line  for  blanket  de- 
posits, is  due  to  one  stratum  being  first  laid  down  and  par- 
tially consolidated  before  the  next  was  laid  later  on  top 
of  it. 

IMPREGNATIONS. 

Rocks  made  up  of  loose  material,  such  as  porous  sand- 
stones and  conglomerates,  are  sometimes  permeated  by  ore 
solutions,  as,  for  example,  the  "  Silver-reef  sandstone  of 
Utah.  Sandstones  are  frequently  impregnated  with  iron 
and  copper  stains.  In  fact,  if  we  consider  that  ore  bodies 
were  deposited  from  aqueous  solutions,  we  have  only  to 
consider  the  various  opportunities  the  rocks  afford  by  their 
texture,  structure,  etc.,  for  this  process.  Veins,  in  a  word, 
are  filled  waterways  of  many  and  various  kinds. 


CHAPTER   VII. 
VARIOUS   FORMS  OF  ORE   DEPOSITS. 

ORE    BEDS. 

"  Ore  beds  are  metalliferous  deposits  interstratified  be- 
tween sedimentary  rocks  of  all  geological  ages.  They  lie 
parallel  to  the  planes  of  stratification  and  follow  all  the 
contortions  of  the  enclosing  strata :  hence  they  are  thrown 
into  folds,  troughs,  arches,  saddles,  or  basins.     The  upper 


h 


! 


\': 


i 


I 


89 


F 


Plate  LIV. 

Faulted  Ore-Beds  in  Anticlinal  and 
Synclinal  Polda. 


portions  of  the  arches  may  often  have  been  removed  by 
erosion,  or  the  strata  may  be  faulted."  The  ore  deposits 
or  beds  at  Aspen  occupy 
a  faulted  synclinal  fold  or 
basin.  The  enclosing  rock 
is  limestone,  in  part  dolo- 
mitic.  At  Leadville  the 
deposits  occupy  part  of  a 
series  of  fp^ulted  anticlinal 
arches  and  synclinal 
troughs,  of  which  the 
Mosquito  range  is  the 
main  axis.  The  beds  lie 
between  dolomitic  lime- 
stone and  sheets  of  por- 
phyry. The  ore  beds  partake  of  all  the  folding,  faulting 
and  other  contortions  which  the  enclosing  rocks  have  suf- 
fered in  the  upheaval  of  the  mountains. 

The  thickness  of  such  deposits  varies  much  and  may 
gradually  thin  out  and  disappear,  but  may  also  continue 
long  enough  for  all  mining  purposes. 

Often  there  are  no  sharp  limits  between  an  ore  bed  and 
the  enclosing  rocks,  or  between  the  ore  bed  and  the  walls, 
if  walls  exist  at  all.  The  ore  appears  to  impregnate  the 
surrounding  rock  by  a  chemical  interchange  between  the 
elements  of  the  rock  and  the  ore.  Such  a  " metasomatic' 
interchange,  "  substitution,"  or  "  replacement"  appears  to 
have  taken  place  in  the  argentiferous  lead  deposits  of 
Leadville  and  Aspen  between  the  ore  and  the  limestones. 

According  to  Phillips,  "  a  true  ore  bed  never  produces  a 
'combed'  or  'ribbon'  structure  made  up  of  symmetrical 
layers,  such  as  is  common  in  so-called  'true  fissure  veins,' 
and  is  usually  without  the  crystalline  texture  observable  in 
veinstones." 


K 


UNSTRATIFIED   DEPOSITS,    FISSURE   VEINS,    ETC. 

Mineral  veins  are  changeable  in  character,  and  their  ap- 
pearances of  a  perplexing  and  complicated  nature.  There 
IS  a  gradual  passage  from  one  form  to  another,  so  that  it  is 
difficult  to  classify  them.  There  is  often  no  such  sharp  dis- 
tinction between  one  form  of  ore  deposit  and  another,  as 


90 


legal  disputes  would  sometimes  demand,  and  a  witness 
should  hardly  be  called  upon  to  assert  on  oath  that  such  a 
vein  is  a  "  true  fissure,"  or  another  a  "  bedded  vein,"  or  a 
third  a  "  segregated  vein."  "  Nature  abhors  straight  lines" 
and  sharp  distinctions,  and  delights  in  blending  one  form 
imperceptibly  with  another. 

Phillips  divides  veins  into  two  classes,  "  regular  and  ir- 
regular veins."  "  Regular  unstratified  deposits  include  true 
veins,  segregated  veins  and  gash  veins.    Irregular  deposits 

i  n  cl  u  d  e  impregnations,  fahl- 
bands,  contact  and  chamber  de- 
posits." 

Veins  are  collections  of  miner- 
al matter,  often  closely  related 
to,  but  differing  more  or  less  in 
character    from,    the    enclosing 
country  rock,  usually  in  fissures 
formed  in  those  rocks  after  the 
rocks  had  more  or  less  consoli- 
dated. 
All  veins  do  not  carry  metals;  some  are  merely  barren 
quartz,  feldspar,  or  calcspar,  like  the  barren  veins  we  so 
often  see  traversing  granite  or  limestone  rocks. 

Veins  may  divide,  "  split  up"  or  thin  out,  and  are  irreg- 
ular in  shape  and  structure,  owing  to  the  irregular  widUi 
of  the  fissures  and  to  other  causes. 


Plate  LV. 

A  Split  Vein. 


DEFINITION    OF   MINING   TERMS. 

The  rock  in  which  a  vein  is  found  is  called  the  "  country 
rock,"  e.g.,  limestone,  granite,  porphyry. 

The  portions  of  country  rock  in  direct  contact  with  the 
vein  are  called  respectively  the  "hanging  wall,"  or  roof, 
and  the  "  foot  wall"  or  floor.  This  is  only  in  inclined  or 
flat  veins,  as  a  vertical  fissure  vein  can  have  neither  roof 
nor  floor,  but  only  two  walls,  east  and  west,  or  north  and 
south,  according  to  the  compass.  The  inclination  of  a  vein 
to  the  horizon  is  its  "  dip."  The  horizontal  direction  of  a 
vein  at  right  angles  to  its  dip  is  its  "strike."  The  latter 
may  commonly  be  observed  along  the  surface  outcrop,  the 
former  either  in  the  workings  of  the  mine  or  where  the 
vein  is  exposed  on  the  side  of  a  canyon. 


\ 


9» 


Both  dip  and  strike  of  a  vein  often  vary  much,  the  for- 
mer with  depth,  the  latter  with  extension  across  the  coun- 
try. A  vein  or  ore  deposit  will  not  unfrequently  begin 
with  a  gentle  dip.  and  increase  rapidly  in  steepness  with 
depth.  The  ore  deposits  on  Aspen  Mountain  commonly 
begin  with  a  dip  of  25°,  and  at  a  depth  of  less  than  a  thou- 
sand feet  reach  60°  or  more. 

As  fissure  veins  commonly  occupy  fault  fissures,  their 
irregularities  in  dip  and  strike  correspond  to  those  we  have 
already  spoken  about,  under  faults 

The  angle  of  Jip  is  usually  taken  from  its  variation  from 
a  horizontal,  not  a  perpendicular  line.  Thus,  a  dip  of  75° 
means  one  that  is  very  steep,  while  one  of  10°  is  a  gentle 
inclination. 

A  layer  cr  sheet  of  clay  called  "  gouge."  or  selvage,  often 
lines  one  or  both  walls  of  a  vein  between  the  country  rock 
and  the  gangue  or  vein  proper.  It  is  derived  from  the  ele- 
ments of  the  adjacent  country  rock,  decomposed  by  water, 
and  sometimes  by  the  friction  of  the  walls  of  the  fissure 
against  one  another,  or  against  the  vein  matter,  in  the 
process  of  slipping  and  faulting,  which  is  often  shown  by 
Its  being  smoothed,  "  slickensided,"  polished,  or  grooved. 
Gouge  often  contains  some  rich  decomposed  mineral  in  it, 
such  as  sulphurets  of  silver.  It  sometimes  occurs  in  the 
heart  of  a  vein,  especially  if  that  vein  has  been  re-opened 
anew  by  movements  of  the  strata.  The  "  Chinese  tallow" 
gouge  of  Leadville  results  from  the  decomposition  of  the 
feldspars  in  the  adjacent  white  porphyry,  and  is  a  hydrous 
silicate  of  alumina. 

In  the  granite  veins  in  Clear  Creek  County  the  gouge  is 
derived  from  the  feldspars  of  the  granite.  Gouge  is  some- 
times useful  in  defining  the  limit  of  the  vein  between 
walls,  thus  preventing  unprofitable  exploration  into  the 
"  country."  It  is  also  a  guide  for  following  down  a  vein 
when  mineral  and  gangue  may  be  wanting  or  obscure. 

Both  walls  are  not  always  clearly  defined  by  slickensided 
surfaces,  by  gouge  or  other  mark,  and  so  at  times  the  vein 
is  lost. 

False  walls,  caused  by  movements  in  the  adjacent  strata, 
by  joints,  etc.,  also  mislead. 

It  is  not  uncommon  for  a  fissure  vein  to  have  but  one 
clearly  defined  wall,  the  other,  if  it  exists,  being  obscured 


99 


or  changed  by  mineral  solutions.  Sometimes  two  cracks 
or  fissures  occur  parallel  to  each  other  and  the  intervening 
country  rock  has  been  altered  and  mineralized  into  a  vein. 
It  is  probably  in  this  way  that  many  wide  veins  were 
formed. 

Mr.  Emmons  has  found  that  fissures  are  formed  by  great 
movements  of  the  earth's  crust  or  by  local  contraction  of 
the  rocks,  and  that  a  fissure  is  not  necessarily  one  with 
well-defined  walls  at  considerable  distances  apart,  filled 

after  the  formation  oi  the  fissure,  but 
that  the  ordinary  cracks  or  joints  in  gran- 
ite quarries,  extending  regularly  to  great 
lengths  or  depths,  illustrate  the  original 
fissures  which  have  been  changed  by 
percolating  waters  carrying  mineral  solu- 
tions into  veins  and  deposits  of  ore.  In 
all  crystalline  and  sedimentary  rocks, 
these  cracks  or  joints  run  parallel  to 
each  other  at  various  distances  apart,  of- 
ten plentiful  and  close  together.  In  cases 
where  percolating  waters  were  charged 
with  the  proper  metals  and  veinstone 
matter  and  the  necessary  chemical  and 
physical  conditions  existed,  the  rocks  ly- 
mg  between  those  cracks  or  joints  were 
altered  into  ore. 

As  one  element  was  dissolved  another  took  its  place;  so, 
according  to  this  authority,  it  would  seem  that  even  a  fis- 
sure vein  may  be  only  a  sort  of  "  metasomatic  replacement" 
of  rock  by  mineral.  Hence,  what  is  commonly  accepted  as 
a  "  wall"  of  a  vein  is  not  necessarily  one,  and  cross-cut- 
ting, in  order  to  determine  the  lateral  boundaries  of  the 
ore,  is  safer  than  to  rely  on  supposed  walls.  A  so-called 
"  slip"  has  often  been  followed  by  a  miner  as  a  supposed 
wall,  until  by  accident  he  broke  through  and  found  good 
ore  on  the  other  side.  If  veins  are  formed  according  to 
Mr.  Emmons'  theory,  the  occasional  loss  of  one  or  both 
walls  is  easily  accounted  for. 

Cross  veins  of  a  more  recent  age  sometimes  cut  or  fault 
an  older  vein.  The  point  of  intersection  is  generally  rich 
in  mineral.  Cross  veins  must  not  be  confounded  with 
"  leaders,"  which  are  the  filling  of  minor  cracks  extending 


Plate  LVI. 

ImpreKnation  of  Rock 
by  Vein. 


off  from  the  vein,  and  are  sometimes  sufficiently  profitable 
to  work.  While  they  sometimes  lead  a  prospector  to  the 
main  vein,  they  may  also  lead  a  miner  underground  astray 
from  the  true  vein. 

The  splitting  of  a  vein  by  a  "  horse,"  or  large  fragment  of 
the  country  lying  in  the  vein,  may  be  mistaken  for  a  true 
cross  vein,  or  the  original  fracture  of  the  fissure  may  have 
been  in  the  form  of  a  star  or  like  the  spokes  of  a  wheel 
radiating  from  the  hub. 

In  such  cases  there  are  no  true  cross  veins.  Hut  when, 
as  in  the  San  Juan  district,  we  have  two  well-defined  sets 
of  veins,  one  striking  northeast  by  southwest,  and  the  other 
northwest  by  southeast,  they  cut  each  other  diagonally,  the 
cut  vein  being  the  older.  These  opposite  sets  of  veins  have 
been  formed  at  different  times.  Many  contain  a  charac- 
teristically different  class  or  variety  of  minerals.  Thus,  in 
Cornwall,  England,  one  set  carries'tin  and  the  other  lead. 


SIGNS    OF   A    TRUE    FISSURE   VEIN. 

True  fissure  veins  show  signs  of  motion  or  slipping  on 
the  sides  of  the  fissure,  such  as 
slickensides,  gouge,  crushed 
walls,  "  horses,"  or  "  breccia," 
the  latter  being  small  portions 
of  the  country  rock  surround- 
ed and  cemented  by  vein  mat- 
ter. In  the  Comstock,  the 
quartz  is  ground  to  powder. 
The  vein  itself,  though  occu- 
pying a  healed  fault  fissure, 
may  be  itself  faulted  by  later 
movements  in  the  mountain 
after  the  vein  was  formed. 
Some  of  the  fissure  veins  on 
Engineer  Mountain,  San  Juan, 
are  so  dislocated. 

The  vein-filled  fissures  be- 
ing a  line  of  weakness,  may  be 
reopened  by  mountain  move- 
ments, and  other  or  different  combinations  of  ore  introduced 
into  the  heart  of  the  vein.     Such  a  reopening  would  be 


Plate  LVII. 

Combed,  Banded  or  Ribbon  Struct- 
ure with  Quartz  Geode. 


-'*    S'« 


94 

marked  by  a  succession  of  "  combs"  or  banded  ribbon-like 
deposits  of  ore,  and  by  gouge  matter. 


OUTCROP   OF   VEINS. 

The  outcrop  of  a  vein  is  that  which  appears  at  the  sur- 
face and  usually  attracts  prospectors  to  the  spot.  Some- 
times it  may  be,  as  in  the  San  Juan  district,  a  bold  vein  of 
hard  white  or  rusty  quartz,  standing  up  in  relief,  by  its 
superior  hardness,  above  the  surrounding  country,  like  a 
low  wall.  Or  again,  in  the  same  district,  from  being  com- 
posed of  softer  or  more  soluble  substances  than  the  pre- 
vailing eruptive  lava  sheets,  instead  of  a  wall,  it  causes  a 
depression  or  trough  on  the  side  of  a  hill,  forming  the 
pathway  for  a  rivulet  and  marked  by  luxuriant  vegetation. 
Commonly  the  outcrop  consists  of  a  decomposed  mass  of 
rock,  stained  with  oxide  of  iron  and  streaked  here  and 
there  with  green  or  blue  carbonate  of  copper,  and  is  called 
"  float"  or  "  blossom"  by  the  miners.  This  float  is  the 
chemically  changed  or  oxidized  portion  of  the  true  and  un- 
changed vein  lying  deeper  below  the  soil.  On  Aspen 
Mountain  the  float  is  generally  a  rough  crystalline  mass  of 
calcspar  and  baryta  stained  with  iron  and  copper. 

In  this  "blossom  rock"  free  gold  is  not  unfrequently 
found,  but  unaltered  sulphides,  such  as  galena  or  iron  py- 
rites, are  rarely  met  with  on  the  outcrop.  In  the  San  Juan 
district,  on  Mineral  Point,  we  have,  however,  found  galena 
at  the  grass  roots,  and  broken  off  large  chunks  of  it  from 
a  quartz  vein  outcropping  on  the  surface. 

In  gold-bearing  veins  such  an  oxidized  condition  is  de- 
sirable if  it  continues  down  to  any  depth,  for,  so  far  as  it 
continues,  the  gold  is  free,  and  the  ore  is  a  free  milling 
one,  easily  treated,  and  often  exceedingly  rich  in  gold,  as 
in  the  celebrated  Bowen  mine  of  Del  Norte ;  but  as  soon  as 
the  hard  white  quartz  and  the  unoxidized  pyrites  of  the 
true  vein  is  reached,  the  ore  is  no  longer  free  milling,  but 
must  be  smelted.  The  gold  may  still  be  found  free,  per- 
haps, in  the  hard  quartz,  but  if  the  pyrites  should  not  prove 
rich  in  gold,  the  palmy  days  of  the  mine  may  be  considered 
as  past.  Many  such  rich  deposits  on  the  surface,  abound- 
ing with  specimens  of  free  gold,  have  proved  great  disap- 
pointments with  depth. 


95 


winni  OF  VF.iNS. 


Veins  mp.y  vary  in  width  or  thickness  from  a  half  inch  to 
a  hundred  feet.     They  also  pinch  or  widen  at  intervals  in 


Plate  LVIII. 

Metalliferous  Veins  Exposed  to  View  near  Howardsville,  San  Juan,  Colo- 
rado, Showing  Two  Systems  of  Fissure  Veins  Crossing  One  Another. 

their  downward  course.     The  widest  "mother"  veins  are 
not  always  the  must  productive,  though  they  are  very  per- 


mm 


96 

sistent  in  length,  and  we  may  suppose  m  depth  also.  In 
the  San  Juan  district  the  "  mammoth"  veins  of  quartz,  often 
a  hundred  feet  wide,  are  not  the  favorites  for  develop- 
ment, the  ore  being  found  too  much  scattered  in  them, 
and  the  development  less  easy  than  in  those  10,  30  or  30 
feet  wide,  where  the  metal  is  more  concentrated.  These 
mammoth  veins  in  the  San  Juan  are  easily  traceable  for 
miles  over  the  surface  of  the  country  and  down  the  sides 
of  the  deep  canyons.  Th'eir  limiting  depth  has  never  been 
reached,  and  probably  never  will  be  by  mining. 


DRFINITION   OF  TRUE   FISSURE   VEINS. 

True  fissure  veins  are  popularly  defined  as  filling  fissures 
of  indefinite  length  and  depth,  commonly  occurring  in 
parallel  systems,  traversing  the  surroundinp^  rocks  inde- 
pendently of  their  structure  or 
stratification,  and  commonly, 
though  not  necessarily,  at  an 
angle  different  from  that  of  the 
stratification — in  other  words, 
cutting  across  the  planes  of 
stratification.  These  veins  orig- 
inated in  fissures,  not  neces- 
sarily wide  open  ones,  but  on 
the  contrary  rather  narrow 
cracks,  descending,  however, 
to  great  depth,  such  as  those 
produced  by  faulting,  or  the 
general  cleavage  lines  of  the 
mountain.  The  latter  may  be  frequently  observed  in  every 
canyon,  and  also  in  the  sedimentary  rocks  of  the  foot-hills 
and' even  along  the  flat  surfaces  of  the  plains.  They  are 
very  conspicuous  in  the  plains  around  Trinidad,  and  are 
there  not  unfrequently  occupied  by  a  series  of  narrow  par- 
allel dykes  of  basalt  instead  of  by  mineral  veins.  Cleavage 
lines  or  joints  are  familiar  to  every  stone-quarry  man. 

These  cracks  are  caused  by  extensive  movements  of  the 
earth's  crust  in  the  process  of  mountain  uplift,  and  also  on 
a  smaller  scale  by  contraction  of  the  rocks  in  cooling  from 
a  heated  or  molten  condition,  or  even  in  consolidating  from 
a  soft  or  muddy  condition. 


Plate  LIX. 

Fissure  Vein  Conforming  in  Part 
to  the  Bedding  Planes  of  Strati- 
fication, in  Part  Crossing  them. 


97 

The  two  waIIs  enclosinp:  a  vein  do  not  jjenerally  concide. 
ns  might  be  expected,  if  the  vein  occupies  a  line  of  fault. 
A  true  fissure  vein  may  in  some  part  of  its  course  coincide 
with  the  dip  of  the  surrounding  strata.  As  the  plane  of 
stratification  or  line  of  division  between  one  stratum  and 
another  is  a  natural  line  of  weakness,  a  crack  once  started 
would  be  liable  to  follow  it  for  some  distance.  And  when 
uplift  occurs  such  places  are  liable  to  slip  one  upon  the 
other,  and  a  true  parting  fiisure  ensues 
conformable  to  the  prevailing  dip.  Such 
a  vein  might  appear  at  first  to  belong  to 
the  class  of  so-called  "  bedded  veins,"  but 
if  with  depth  it  should  be  discovered  to  be 
cutting  across  the  strata  it  would  be  pro- 
nounced a  "  true  fissure  vein."  The  ap- 
pearance of  slickensides  or  other  signs 
of  motion  on  the  walls  of  the  apparent- 
ly "  bedded  portion"  would  then  prove  it 
to  belong  to  the  " true  fissure'  class,  and 
that  actual  fissuring  had  taken  place  prior 
to  the  vein-filling. 


Plate 


CAUSE   OF    I'OCKETS    IN    FISSURE    VEINS. 

As  a  fault  fissure  in  its  downward 
course  usually  pursues  a  zigzag  rather 
than  a  straight  course  with  smooth  sur- 
faces on  either  side  of  the  crack,  the  in- 
equalities of  one  face  of  the  crack  are 
brought  into  opposition  to  the  inequali- 
ties on  the  other  face,  as  one  or  the  other 
side  of  the  fault  slips  up  or  down,  and 
thus  are  produced  pinches  and  wide  cavi- 
ties, which  give  rise  to  the  "  pinches"  and 
"  bonanza  pockets"  so  common  in  fissure 
veins.  A  so-called  true  fissure  vein  may 
sometimes  have  advantages  over  some  other  forms  of  vein 
occurrence,  from  its  persistency  and  comparative  regu- 
larity to  gn*eat  depths.  It  must  not,  however,  be  expected 
that  it  will  continue  equally  rich  or  equally  poor  through- 
out its  course.  There  may  be  comparatively  barren  spots 
and  rich  spots,  pinches  and  widenings,  local  c  >i  ibinations 

7 


Pocket  and  Pinches 
resulting  from  Slip- 
pingf  of  Uneven 
Walls  of  Fissure. 


of  richer  or  poorer  varieticH  of  mineral. 
rule  is  not  liicely  to  entirely  give  out. 


nut  thu  vein  its  h 


RICHNESS   WITH    DKPTH. 

There  is  no  scientific  reason  why  a  vein  should  "  grow  in 
richness  and  size  with  depth."  This  is  a  popular  fallacy, 
originating  from  the  now  less  accepted  theory  that  veins 
were  formed  by  thf»  precipitation  of  precious  metals,  by 
heated  rising  waters  or  vapors,  and  hence  that  the  greater 
concentration  would  take  place  at  greater  depths.  The 
"  lateral  secretion"  theory,  now  by  some  accepted,  ascribes 
the  deposition  of  ore  to  solvent  waters  reaching  the  vein 
from  ground  quite  near  to  it,  and  coming  naturally  from 
above  and  the  sides  quite  as  often  as  it  is  ejected  ttpward 
by  pressure  from  below. 

In  Idaho  Territory,  says  Mr.  A.  Williams,  "  the  rule  is 
rather  that  veins  grow  less  rich  and  strong  with  depth, 
though  strong  veins  may  continue  metalliferous  to  a  greater 
depth  than  mining  can  ever  reach. 

The  thickness  of  the  earth's  crust  which  we  are  able 
to  explore  is  very  limited.  Increase  of  heat,  as  in  the  deep 
Comstock  mine,  and  other  natural  difficulties,  limit  us  to  a 
few  thousand  feet — 3,000  at  most.  These  deep  mines  have 
not,  as  a  rule,  proved  richer  with  depth,  but  to  the  contrary. 
Some  veins  have  been  worked  through  alternate  zones  of 
richness  and  barrenness.  The  Comstock,  which  has  been 
opened  for  four  miles  in  length  and  to  a  depth  of  3,000  feet, 
snows  the  ore  bodies  to  be  scattered  irregularly  and  the 
barrenest  ground  is  at  the  bottom.  On  the  other  hand, 
some  of  the  most  celebrated  mines  derived  their  wealth 
from  rich  ores  encountered  near  the  surface  and  have  proved 
most  disappointing  with  depth." 

Atmospheric  action  for  a  long  period  has  often  reduced 
the  ore  to  its  richest  compound,  and  when  the  hard  mate- 
rial is  reached  leanness  sets  in.  This,  as  we  have  observed, 
is  commonly  the  case  with  gold  veins.  The  richness 
of  the  Leadville  mines  is  derived  from  their  decom- 
posed compounds.  Again,  as  the  surface  crust  can  be  so 
little  explored  by  mining,  it  is  to  be  remembered  that  the 
erosion  by  glaciers  and  waters  has  already  removed  thou- 
sands of  feet  of  the  vein,  so  that  we  are  able  to  examine 


99 

only  a  small  fraction  of  it,  while  an  unknown  ({uantity  lies 
in  thi"  depths  below.  If  these  veins,  then,  continue  to  the 
supposed  great  depths  below,  we  are  very  far  from  their 
starting  point,  and  erosion  having  rem»)ved  their  upper 
portions,  we  cannot  find  their  surface  finishing  point;  in 
other  words,  it  is  not  n  fresh  "ready  made"  vein  we  find, 
but  portions  of  an  old  vein  already  extensively  mined  by 
the  processes  of  nature. 

So  far  as  our  experience  goes  in  Colorado,  after  a  moder- 
ate depth  is  reached  below  surface  action,  or  belt>w  the 
"  water  level,"  a  fissure  vein  may  grow  richer  or  poorer, 
wider  or  narrower  with  depth,  without  any  law  except 
local  experience  in  a  district. 

•  VKiNs  IN  c.wours. 

Fissure-veins  occur  in  clusters  and  nearly  parallel  groups, 
forming  a  mining  district,  and  again  in  that  district  certain 

?ecuHar  veins  may  be  grouped  together,  ftirming  a  "  belt  ' 
'hus,  Boulder  district  occupies  a  certain  isolated  area,  out- 
side of  which  few  mineral  deposits  occur  for  a  long  dis- 
tance. We  have  also  in  that  district  several  distinct  belts 
carrying  different  characteristic  ores,  such  as  the  telluride 
belt,  marked  by  rare  telluride  deposits,  the  pyritiferous 
gold-bearing  belt,  and  the  argentiferous  galena  belt.  The 
Central  City  region  is  characterized  by  auriferous  pyrites 
belts,  Georgetown  district,  not  far  distant,  by  argentifcr- 
t)us  belts,  and  Idaho  Springs,  lying  between  the  two,  by 
both  gold  and  silver  belts. 


CHAPTKR    VIII. 
RELATION   OF   VEINS   TO   ERUPTIVE   FORCES. 

The  ultimate  cause  of  the  richness  in  veins  of  a  district 
or  locality  is,  that  local  dynamic  and  eruptive  forces  were 
more  energetic  there  than  elsewhere,  causing  great  disturb- 
ance of  the  rocks,  accompanied  by  fissures  and  eruptions 
of  porphyry. 

Thus  at  Leadville,  the  Mosquito  range  is  violently  folded 
.^nd  fractured,  eruptive  rucks  have  issued  abundantly,  and 


>li 


lOO 


associated  with  such  phenomena  we  find  great  lead  and 
silver  deposits. 

Further  south  the  great  San  Juan  district  is  split  up  in 
an  extraordinary  manner  with  great  fissure  veins.  The 
region  is  an  eruptive  one,  consisting  of  prodigious  flows  of 
eruptive  rocks,  traversed,  not  unfrequently,  by  newer  erup- 
tive dykes. 

In  the  Gunnison  district  the  strata  have  been  overturned, 
disturbed,  folded,  and  faulted  in  an  extraordinary  manner 
by  the  intrusion  of  great  masses  of  eruptive  rock  forming 
the  peaks  of  the  Elk  Mountains.  The  strata  everywhere 
are  riddled  by  dykes  or  intrusive  sheets,  and  the  evidence 
of  heat  is  apparent  in  the  general  metamorphism  of  the 
entire  region.  Mineral  veins  abound.  The  same  phenom- 
ena are  repeated  more  or  less  in  the  neighboring  region 
around  Aspen,  and  at  Pitkin  and  Tincup. 

At  Boulder,  Central,  and  Georgetown  there  is  a  concen- 
tration of  eruptive  dykes  locally  in  each  district,  and  a  few 
dykes  or  eruptive  rocks  outside  of  those  districts.  On  the 
other  hand,  we  have  no  ore  deposits  in  the  undii.turbed 
rocks  of  the  plains  or  the  flat  basins  of  our  parks,  and  no- 
tably our  mining  districts  are  for  the  most  part  well  into 
the  core  of  the  mountains,  where,  in  the  nature  of  things, 
folding,  crumpling,  faulting,  eruptions,  and  metamorphic 
heat  were  more  energetic  than  along  the  flanks  and  foot- 
hills of  the  range  which  have  usually  proved  unproductive. 

The  older  eruptive  rocks,  such  as  the  quartz,  porphyries, 
and  diorites  of  the  Leadville,  South  Park,  and  Gunnison  dis- 
tricts, are  more  favorable  to  the  production  of  ore  deposits, 
as  a  rule,  than  the  more  modernly  erupted  lavas,  such  as 
basalt  or  dolerite,  which  we  commonly  find  occurring  in 
dykes  and  surface  overflows,  traversing  cr  capping  our 
Cretaceous  and  Tertiary  coal  fields  along  the  foothills  as 
at  the  Table  Mountains  at  Golden  and  Trinidad. 

Some  of  the  lighter  colored  and  somewhat  recent  lavas 
like  the  tufaceous  rhyolite,  which  caps  so  many  of  the 
Tertiary  mesas  on  the  Divide  between  Denver  and  Colo- 
rado Springs,  have  also  hitherto  proved  barren.  Yet  the 
volcanic  rhyolites,  andesites  and  phonolites  of  Silver  Cliflf, 
Cripple  Creek  and  Creede  are  productive  of  both  gold  and 
silver.  A  large  portion  of  the  eruptive  rocks  of  the  San 
Juan  region,  productive  of  gold  and  silver-bearing  fissure 


I^I 


veins,  are  in  andesitic  breccias  of  comparatively  modem 
date.  The  older  eruptive  rocks,  as  we  have  stated,  are 
nearly  all  of  an  intrusive  character,  never  having  reached 
the  surface,  while  the  newer  ones  bear  evidence  of  having 
flowed  over  the  country  like  modem  lava-streams,  as  is 
shown  by  spongy  scoria  on  their  surface,  and  may  be  called 
"effusive." 

In  Colorado  the  ore  body  is  not  usually  found  in  the  heart 
of  an  eruptive  sheet  or  dyke  of  porphyry,  so  much  as  at  the 
line  of  its  contact  with  some  other  rock,  such  as  limestone, 
granite  or  gneiss. 

CONTACT    DEPOSITS. 

The  "  contact"  ore  deposits  of  Leadville  occur  at  the  con- 
tact of  quartz,  porphyry  and  dolomitic  blue  limestone. 

Some  of  the  veins  at  Boulder,  Central  and  Georgetown 
are  at  the  contact  of  porphyry  and  granite  or  gneiss. 

Exceptions  occur,  however,  where  mineral  is  found  either 
in  the  heart  of  a  dyke,  or  the  whole  dyke  may  be  so  impreg- 
nated ^s  to  constitute  in  a  sense  a  vein.  These  excep- 
tions are  generally  confined  to  pyritiferous  gold  deposits, 
and  telluride  goM  deposits  as  at  Cripple  Creek. 


GOLD-BEARING    DYKES. 

Suppose  a  dyke  or  mass  of  eruptive  rock  to  be  thoroughly 
impregnated  with  gold-bearing  pyrites.  Near  the  surface 
and  often  for  a  considerable  depth  the  rock  is  decomposed 
and  the  pyrites  oxidized  into  rusty  iron  ore,  liberating  the 
Hold  which  is  entangled  in  the  "  gossan"  in  wires,  flakes  or 
even  small  nuggets.  As  long  as  this  decomposed  or  oxi- 
dized state  continues,  the  ore  is  free  milling,  but  with 
depth  the  dyke  is  found  in  its  primitive  hardness,  studded 
with  iron  pyrites,  which  may  or  may  not  prove  rich  enough 
for  the  more  expensive  treatment  of  smelting.  Such  gold- 
bearing  dykes  are  found  at  Breckenridge,  South  Park,  also 
in  Idaho  Territory,  Cripple  Creek,  Colorado,  and  in  old 
Mexico,  and  many  other  gold-bearing  regions. 

The  Printer  Boy  gold  mine  at  Leadville  is  a  vertical  de- 
posit in  a  jointing  or  fracture  plane  in  a  dyke  of  quartz- 
l)orphyry,  rusty  and  much  decomposed  near  the  surface, 
where  it  yielded  free  gold ;  with  depth  this  passes  into  cop- 


1 01 


9ut090nt 


per  and  iron  pyrites.     The  vein  is  from  an  inch  to  four  feet 
in  width;  stringers  carrying  ore  extend  into  the  porphyry, 

which  is  highly  charged  with 
pyrites,  which  doubtless  supplied 
the  vein  with  mineral  through  the 
agency  of  surface  waters.  In  Ari- 
zona, near  Prescott,  at  the  Lion 
mine  we  find  a  green  dyke ».  f  erup- 
tive diorite  penetrating  granite. 
This  dyke  is  traversed  by  nu- 
merous small  veins  of  white  quartz 
which  near  the  decomposed  and 
rusty  surface  are  rich  in  free  gold. 
At  slight  depth  the  quartz  veins 
become  charged  with  unoxidized 
iron  pyrites  sufficiently  rich  in 
Ske';Xw,>,Jox1di"ld'"in§  gold  to  merit  treatment  by  smelt- 
Unoxidized  Portions.  ing.     The  surface  ore  is  treated 

by  a  simple  "  arrastra,"  and  is,  of 
course,  free  milling.  The  gold  seems  to  be  mostly  con- 
fined to  the  quartz  veins. 


Plate  LXI 

<»old    Vein    or    Gold    Bearin 


FISSURE   VEINS    IN    IGNEOUS    AND   GRANITIC    ROCKS. 

The  San  Juan  district  is  an  exceptional  case  where  im- 
mense numbers  of  fissure  veins  penetrate  igneous  eruptive 
sheets.  The  fissure  veins  consist  of  hard  gray  jaspery 
quartz  traversing  lava  sheets  whose  united  thickness  is 
from  2,000  to  3,000  feet.  The  veins  produce  lead,  bis- 
muthinite,  gray  copper  and  other  silver-bearing  ores. 

In  Colorado  true  fissure  veins  are  most  characteristic  of 
the  Archaean  granitic  series.  In  fact,  all  the  veins  in  that 
series  are  fissure  veins.  Locally  they  occur  as  in  the  San 
Juan,  cutting  through  eruptive  rocks.  Outside  of  these 
formations  few  true  fissure  veins  occur. 

An  exception  may  be  made  of  the  Gunnison  and  Elk 
Mountain  region  where  the  fissures  traverse  all  the  forma- 
tions from  Archaean  granite  to  the  top  of  the  Cretaceous 
coal  beds.  Nearly  all  other  mineral  occurrences,  such  as 
those  in  the  limestone  regions,  come  under  the  class  of 
bedded-veins  or  blanket-veins,  pipe- veins  or  "  poc  ets,"  and 
show  none  of  the  characteristics  of  slipping  motion  or  fissure 


103 


action.  Under  this  latter  class  the  Leadville  and  Aspen 
deposits  may  be  grouped. 

Ore  deposits  commonly  occur  at  the  junction  or  contact 
of  two  dissimilar  rocks,  as  between  quartzite  and  limestone 
or  limestone  and  dolomite. 

Lodes  occur  also  between  the  stratification  planes  of  the 
same  class  of  rock,  sandwiched  in  between  two  layers  of 
limestone,  and  sometimes  impregnating  the  layers  on  either 
side  for  some  distance  from  the  dividing  line  between  the 
two  strata,  which  is  commonly  the  line  of  principal  con- 
centration of  ore,  and  often  descend  from  this  concen- 
tration line,  through  the  medium  of  cross  joints,  to  form 
large  pockets  in  the  mass  of  the  limestone.  The  Aspen 
and  Leadville  deposits  are  of  this  character.  Also  when 
ore  bodies  occupy  a  true  fissure,  /.  e.,  one  cutting  across 
the  stratification  planes,  they  may  locally,  for  a  short  dis- 
tance, impregnate  the  adjacent  walls  or  country  rock  more 
or  less.  Our  fissure  veins  in  granite  and  gjneiss  often  im- 
prep:nate  the  walls  to  a  small  extent. 

>■  neral  deposits  favor  as  a  rule  the  older  rocks,  such  as 
the  .irchaean  and  Paleozoic  series,  propably  because  heat 
and  metamorphic  action  are  commoner  in  these  older  rocks, 
which  have  felt  all  the  throes  of  the  earth  from  past  to 
present  times,  than  in  the  more  recent  ones,  and  such  cir- 
cumstances, as  we  have  stated,  are  peculiarly  favorable  to 
vein  formation  and  mineral  deposition. 

The  bulk  of  our  precious  minerals  in  Colorado  comes 
from  the  older  Archaean  and  Paleozoic  series  of  rocks,  the 
exception  being  the  Gunnison  region  around  Crested  Butte, 
Irwin  and  Ruby,  where  ore  comes  from  fissure  veins  in  the 
Mesozoic  Cretaceous  rocks.  The  exception  is  accounted 
for  by  the  local  metamorphism,  heat  and  eruptive  phenom- 
ena of  that  region. 

The  veins  in  the  San  Juan  have  also  been  ascribed  by 
some  to  the  Tertiary  Period,  owing  to  their  occurrence  in 
certain  supposed  Tertiary  lavas  covering  that  district. 

Besides  heat,  metamorphism,  dynamical  disturbances 
and  eruptive  agencies,  other  minor  circumstances  may  favor 
ore  deposition.  Certain  rocks,  such  as  limestones,  may 
offer,  by  their  tendency  to  solubility  and  chemical  reac- 
tions, more  favorable  conditions  than  others  for  mineral 
solutions  to  deposit  by  "  metasomatic"  interchange  between 


II 
0-' 


li 


.>^ 


ro4 


mineral  and  limestone,  until  the  limestone  is  gp-adually 
replaced  by  ore,  much  in  the  same  way  as  the  elements  of 
a  water-logged  trunk  of  a  tree  are  replaced  by  silica  in  the 
process  of  fossilization. 


1 1 


It 


CHANGE    OK    MINERALS    WITH    DEPTH. 

Lodes  often  change  in  the  character  of  their  minerals 
with  depth,  not  only  after  they  have  left  the  zone  of  second- 
ary decomposition  and  surface  action,  but  also  far  below  it. 
Thus,  in  the  San  Juan,  some  of  the  mines  abound  in  zinc- 
blende  near  the  surface,  which  with  depth  almost  disap- 
pears, gfiving  place  to  gray  copper  and  other  superior  ores. 
In  Cornwall,  England,  the  shallow  workings  yield  copper, 
and  with  depth,  tin ;  and  locally  many  such  changes  may 
characterize  a  particular  district,  but  cannot  be  formulated 
as  a  rule  for  other  localities. 


INFLUENCE    OK    COUNTRY     ROCK. 

In  most  mining  regions,  to  which  Colorado  is  no  excep- 
tion, a  relation  has  been  observed  between  varieties  of 
"  country  rock"  and  ore  deposits.  Veins  in  passing  from 
one  country  rock  to  another  are  liable  to  change  in  the  size 
or  variety  of  the  ore,  widening  in  connection  with  some 
rocks,  and  pinching  or  growing  narrower  in  connection  with 
others. 

Certain  rocks  are  notorious  ore-bearers,  whilst  others  are 
notoriously  barren  over  large  regions,  or  in  special  localities. 

The  presence  of  certain  rocks  adjacent  to  other  diflferent 
rocks  has  an  enriching  tendency  on  the  ore  bodies. 

As  regards  rocks  that  are  good  ore-carriers  or  receptacles 
of  particular  classes  of  ore  in  Colorado,  we  may  say :  That 
quartzites  and  silicious  rocks  generally  carry  more  pyrites, 
and  are  gold-bearing. 

That  veins  in  granitic  rocks  carry  a  greater  variety  of 
minerals  than  others,  and  may  be  both  gold  and  silver 
bearing. 

That  certain  limestones  carry  much  argentiferous  galena. 

That  sandstones  and  other  unaltered  rocks  carry  little 
ore  of  any  kind. 


'05 


The  influence  of  country  rock  on  veins  may  be  from  sev- 
eral different  causes,  for  instance  : 

Certain  rocks  are  by  their  structure  better  adapted  than 
others  for  forming  regular  fissures.  Thus,  massive  lime- 
stone is  better  fissured  than  slate  or  shale,  leaving  wider 
open  spaces  for  the  ore  to  collect  in. 

Other  rocks  may  be  more  porous,  and  admit  mineral  solu- 
tions through  their  pores.  Of  such  a  kind  are  some  of  our 
porphyries,  andesites  and  phonolites. 

Others,  like  limestone,  are  easily  acted  upon  by  solutions 
dissolving  out  the  rock  and  replacing  it  with  mineral  by 
substitution. 

Some  are  better  conductors  of  heat,  and  therefore  would 
assist  chemical  action  and  mineral  solution. 

And  lastly,  if  modern  theories  of  "  lateral  secretion"  be 
true,  viz. :  That  most  ore  comes  from  the  adjacent  country 
rock  and  is  precipitated,  substituted,  or  collected  in  the 
vein  fissure,  and  further,  that  the  metals  themselves  are 
derived  from  certain  metallic  elements  in  the  ordinary  con- 
stituent minerals  of  the  country  rock,  such  as  mica,  horn- 
blende, or  augfite,  it  is  clear  that  a  rock  composed  largely 
of  such  minerals  would  be  liable  to  influence  the  vein  as 
an  ore  generator.  Granite,  porphyries  and  andesites  are 
largely  composed  of  these  minerals. 

The  frequent  presence  of  eruptive  porphyry  rocks  near 
veins  and  ore  deposits  in  Colorado  shows  that  they  have  an 
important  influence  on  those  deposits,  which  may  be  of 
various  kinds. 

First,  that  in  their  component  minerals  and  mass  they 
actually  contain  the  elements  of  the  precious  metals  sub- 
sequently deposited  in  another  form  in  the  fissure  vein  or 
in  the  soluble  limestone  in  contact  with  it. 

Second,  by  the  heat  which  they  retain  for  a  long  time 
after  they  have  congeakd  and  hardened,  they  would  assist 
in  the  reactions  of  any  chemical  or'  mineral  solutions  that 
might  be  on  hand.  Lava,  at  the  time  of  its  eruption,  is 
always  highly  charged  with  steam  and  other  gases.  By 
reason,  also,  of  the  chemical  composition  of  porphyry, 
waters  passing  through  it  would  be  alkaline  and  assist  in 
dissolving  silica  and  other  gangue  or  veinstone  matter, 
and  when  the  porphyry  has  thoroughly  cooled  it  is  exceed- 
ingly porous,  and  being  much  jointed  and  cross-fractured. 


^ 


106 


becomes  like  a  great  sponge  for  the  absorption  of  all  sur- 
face waters.  This  may  be  noticed  at  Aspen,  where  all 
the  mines  that  are  at  present  penetrating  through  the 
"  porphyry  cap"  are  much  troubled  with  water,  far  more  so 
than  in  the  underlying  limestone.  Surface  waters,  then, 
becoming  alkaline  by  passing  through  this  rock,  and  also 
more  or  less  charged  with  carbonic  acid,  chlorine,  and 
other  solvents,  would  be  ready  to  dissolve  both  gangue 
and  vein  ingredients  out  of  the  porphyry  and  redeposit 
them  in  the  vein  fissure,  or,  by  metasomatic  substitution, 
in  the  limestone  usually  beneath  it. 

Water  circulating  in  fissures,  changes  or  dissolves  the 
ingredients  of  the  surrounding  rock.  The  rocks  enclosing 
lodes  are  always  so  altered,  and  this  decomposition  and 
alteration  is  not  always  merely  local  or  confined  to  the 
close  proximity  of  the  ore  body,  but  we  often  find  a  whole 
mining  district,  such  as  Leadville,  Aspen  and  San  Juan, 
pervaded  by  this  feature.  So  much  is  this  the  case  that  it 
is  often  difficult  to  get  a  fresh,  unaltered  specimen  of  por- 
phyry or  some  other  country  rock  within  the  district. 

The  brilliant  red,  yellow  and  maroon  tints  that  color  so 
much  of  the  mining  district  of  San  Juan  result  from  the 
oxidation  of  pyrites  and  other  iron-bearing  minerals  per- 
vading the  eruptive  rocks,  and  it  is  noticeable  that  this 
color,  resulting  from  alteration  and  decomposition,  is  most 
prominent  in  those  parts  where  lodes  have  been  discovered, 
as,  for  example,  the  gorgeous  tints  of  the  Red  Mountain 
area  around  the  celebrated  "  National  Belle,"  "  Yankee 
Girl,"  and  Iron  ton  mines,  between  Silverton  and  Ouray. 
The  rocks  in  Geneva  Gulch,  Hall's  Valley,  Buckskin  Can- 
yon, and  in  other  mining  centers,  display  the  same  beauti- 
ful tints  of  oxidation  in  the  vicinity  of  the  mines. 

"  In  lodes  a  mutual  exchange  takes  place  through  the 
reaction  of  the  ingredients  of  the  rock  and  the  materials  of 
the  vein.  Thus,  when  water  containing  carbonates  comes 
in  contact  with  rocks  or  minerals  containing  alkalies,  a 
chemical  reaction  takes  place.  When  these  last  are  com- 
bined with  silicic  acid,  these  silicates  are  decomposed  by 
the  carbonic  acid  and  the  bicarbonates.  This  explains 
both  the  crystallizing  out  of  the  carbonates  and  the  so  fre- 
quent decomposition  of  rocks  containing  lodes,  especially 
those  which,  like  our  veins  in  granite,  are  feldspathic." 


I07 

The  same  principle  applies  to  other  ores  and  minerals 
in  lodes.  Thus  the  precious  metals,  in  the  mines  of  Lead- 
ville  in  their  original  condition,  have  been  proved  by  depth 
to  have  been  in  a  sulphide  state,  such  as  iron  pyrites  (sul- 
phide of  iron),  or  galena  (sulphide  of  lead,)  etc.  Surface 
waters  charged  with  carbonic  and  other  acids,  passing 
through  the  overlying  porous  alkaline  porphyry  and  enter- 
ing the  underlying  limestones,  have,  as  we  have  previously 
observed,  changed  the  sulphides  into  sulphates,  oxides, 
and  carbonates. 

The  presence  of  a  dyke  near  to  or  cutting  a  vein  has 
been  found  often  to  enrich  the  latter  at  the  point  of  contact. 

In  the  "  Colorado  Central"  mine  at  Georgetown  a  narrow 
dyke  of  brown  obsidian  traverses  a  large  dyke  of  ore-bear- 
ing porphyry.  The  valuable  ore  is  found  close  to  the 
obsidian  dyke.  This  might  be  the  result  of  greater  heat 
at  that  point.  The  "  black  dyke"  in  the  Comstock  mine  is 
a  somewhat  similar  case. 


PREJUDICE     IN     FAVOR    OF    AND    AGAINST    CERTAIN     ROCKS. 

There  is  often  a  prejudice  amongst  miners  in  favor  of 
certain  rocks  and  formations,  and  against  others.  Miners 
who  have  worked  perhaps  in  the  g^eat  Comstock  mine  of 
Nevada  or  the  Leadville  mines  of  Colorado,  or  the  fissure 
veins  in  granite  of  the  Old  World,  are  apt  to  look  out  for 
and  favor  certain  rocks  and  formations  they  find  like  those 
they  have  been  accustomed  to.  Thus,  as  Mr.  Williams 
says :  "  The  peculiar '  porphyry'  of  the  Comstock  was  hunted 
up  in  other  districts,  but  did  not  prove  metalliferous.  Solid 
granite  was  looked  upon  by  others  as  unfavorable,  gen- 
erally, because  locally  some  granite  above  the  gold  belt  of 
California  had  proved  barren.  Yet  some  of  our  best  veins 
are  in  granite. 

"  Limestone  was  at  one  time  a  very  unpopular  rock  and 
supposed  only  locally  to  produce  lead,  till  the  discoveries 
of  Leadville,  and  Eureka,  Nevada,  overturned  the  scale  in 
its  favor." 

In  the  Leadville  "  excitement"  not  only  was  the  particu- 
lar Carboniferous  limestone  of  Leadville  hunted  for  and 
prospected,  but  every  other  limestone  in  the  South  Park 
region,  no  matter  what  its  geological  age  or  position,  was 


^v 


io8 


extensively  prospected  without  results,  miners  not  recog- 
nizing the  fact  that  it  was  not  limestone  generally  that  pro- 
duces rich  ores,  but  a  particular  limestone  of  a  particular 
geological  period  (the  Lower  Carboniferous)  not  over  200 
feet  thick,  that  happened  locally  to  be  rich  near  Leadville, 
and  the  reason  of  its  being  locally  rich  at  that  point  was 
owing  to  the  concentration  of  eruptive  energy  at  that  point 
and  the  intrusion  of  an  unusual  amount  of  porphyries, 
which  in  point  of  fact  are  far  more  responsible  for  the  ore 
than  the  limestone,  which  happens  to  be  merely  the 
receptacle. 

It  was  also  quite  common  after  the  Leadville  xcitement 
to  find  shafts  in  all  sorts  of  improbable  and  hopeless  locali- 
ties, whose  owners  would  tell  you :  "  At  Leadville  it  didn't 
matter  where  a  man  'went  down.'  It  was  all  luck  whether 
you  'struck  it*  or  not,  and  so  they  might  as  well  'go  down' 
where  they  were  as  elsewhere."  It  was  often  said  "  that 
Leadville  had  exploded  all  so-called  scientific  theories  about 
ore  being  in  oiic  formation  or  locality  more  than  another. 
It  was  all  a  case  of  luck." 

The  excuse  for  this  is  to  be  found  in  the  fact  that  in  the 
immediate  vicinity  of  Leadville  it  did  scarcely  matter 
"  where  you  went  down,"  seeing  that  that  area  was  prac- 
tically underlaid  by  bedded  sheets  of  mineral,  but  that  such 
would  be  the  case  elsewhere  and  everywhere  or  "nywhere, 
experience  unfortunately  has  shown  to  be  untrue.  It  is  not  a 
particular  rock  or  formation,  but  a  combination  of  favorable 
circumstances,  that  alone  can  make  a  rich  mining  district. 

As  experience  advances,  geologists  and  miners  have 
proved  that  ore  deposits  have  a  mtch  wider  range  than 
was  once  supposed.  F'ormerly  only  the  Archaean  g^ranite 
series  was  supposed  capable  of  bearing  ore  deposits, 
because  in  the  Old  World,  tin,  copper  and  lead  came  prin- 
cipally from  fissure  veins  in  those  rocks.  Then  deposits 
were  found  in  the  Paleozoic  series  and  supposed  to  ascend 
no  higher.  But  in  the  present  day,  and  even  in  Colorado, 
they  are  traceable  even  to  the  Tertiary. 

It  is  not  the  rock,  nor  the  age,  but  a  combination  of  cir- 
cumstances, principally  heat  and  metamorphism,  that  may 
make  any  rock  of  any  period  an  ore-bearing  one.  And  in 
prospecting  in  new  regions  it  is  these  combinations  rather 
than  any  particular  rock  that  should  be  looked  for. 


109 


STRIKE     ANU    DIP    OF    VEINS. 

The  dip  of  veins  approaches  more  nearly  the  vertical 
than  the  horizontal,  usually  from  75°  to  verticality. 
Nearly  all  our  ore  deposits,  in  Colorado,  even  those  of  the 
bedded  class,  dip  more  or  less  steeply  from  25°  to  75°. 

For  a  few  feet  from  the  surface,  on  the  steep  slope  of  a 
mountain,  it  is  common  to  find  an  ore  deposit  dipping  quite 
gently  or  even  folded  over  and  dipping  in  a  contrary  direc- 
tion to  that  which  it  assumes  with  depth.  This  appears  to 
arise  from  the  weight  of  the  strata  above  it  tending  to  bend 
it  over  downward  in  tl     direction  of  the  slope  of  the  hill. 

Th  re  is  generally  a  prevailing  dip  and  strike  amongst 
a  number  of  parallel  fissure  veins  of  a  district.  In  the  San 
Juan,  the  bulk  of  the  fissure  veins  have  a  prevailing  north- 
easterly strike  and  dip  to  the  southeast.  The  angle  of 
dip  is  generally  between  60°  and  verticality. 

CROSS-CUTTING     UNCERTAIN. 

The  dip,  as  we  have  said,  not  unfrequently  changes  con- 
siderably with  depth,  usually  becoming  more  and  more 
vertical.  From  the  degree  of  uncertainty  as  lo  the  con- 
tinuity of  the  dip,  it  is  not 
always  safe,  on  the  discov- 
ery of  an  outcrop,  to  endea- 
vor to  cut  it  at  a  much  low- 
er point,  so  as  to  get  the 
coveted  depth,  and  better 
opportunities  for  stoping. 
drainage  and  other  devel- 
opments of  the  mine.  Ow- 
ing to  a  change  of  dip  or 
fault,  perhaps,  the  miner 
may  liave  to  make  a  much 
longer  cross-cut  tunnel  than 
he  had  calculated  upon  be- 
fore striking  the  vein. 
Sometimes,  too,  he  may 
miss  the  vein  altogether, 
cutting  it  perhaps  at  some 

point  where  it  is  exceedingly  thin  or  poor,  so  poor  in  fact 
that  he  passes  through  it  without  noticing  it  or  believing 


Plate  LXIl. 

Showing  How  Cross-cut  Tunnels  and 
Shafts  May  Miss  Veins  by  Change  of 
Dip  or  Faulting. 


no 


it  to  be  the  same  vein  whose  outcrop  looked  so  promising 
on  the  surface.  Cross  tunnels  through  "  dead  rock"  should 
hardly  be  undertaken  until  the  vein  has  been  proved  to  be 
a  strong  one  for  a  considerable  depth.  As  we  have  already 
shown,  great  depths  may  not  after  all  be  so  desirable  in 
even  a  fissure  vein,  as  there  is  no  certainty  whatever  about 
veins  becoming  richer  or  poorer  with  depth.  Extensive 
cross-cut  tunnels  have  seldom  proved  paying  concerns. 
The  greatest  in  the  United  States,  the  Sutro  tunnel,  six 
miles  in  length,  which  tapped  the  Comstock  fissure  at  a 
depth  of  2,000  feet,  did  not  prove  a  financial  success,  and 

had  it  tapped  the  fissure  still 
lower,  at  3,000  feet,  it  would 
have  found  the  vein  in  the 
impoverished  condition  it  is 
today.  It  is  not  uncommon 
for  a  miner  to  strike  a  rich 
outcrop  on  the  top  of  some 
mountain,  and  on  the 
strength  of  its  richness  in- 
duce a  company  to  run  a  long 
cross-cut  tunnel  in  "  dead 
rock"  half  through  the  moun- 
tain to  cut  this  vein,  and  the 
company's  resources  are 
nearly  exhausted  in  so  do- 
ing, while  the  vein  itself 
gives  no  returns,  owing  to  its  being  left  idle.  Finally, 
perhaps,  the  vein  is  missed,  or  if  struck,  proves  far  poorer 
than  was  anticipated.  Of  course  there  are  exceptions 
where  cross-cut  tunnels  in  "  dead  rock"  may  be  advisable. 

If  a  fissure  vein,  as  in  the  San  Juan,  should  outcrop  near 
the  top  of  a  mountain  and  be  exposed  on  its  dip  all  the  way 
to  the  bottom,  there  may  be  some  reason  for  opening  a 
tunnel  in  it  near  the  base,  thereby  facilitating  drainage, 
development  and  exportation.  In  that  case  the  miner  is  on 
the  vein,  with  no  fear  of  losing  it ;  but  even  here,  there  is 
no  guarantee  that  it  will  prove  rich  all  the  way  to  its  out- 
crop a  thousand  feet  above.  "  Follow  your  ore.  and  be 
careful  how  you  leave  it  for  any  experimental  theories,"  is 
a  common  and  wise  saying  among  experienced  miners. 
We  remember  a  tunnel  in  the  Gunnison  region  which  was 


Plate  LXHI. 

Fissure  Vein  Exposed  from  Outcrop 
to  Dip. 


1 1 1 


run  several  hundred  led  at  a  cost  of  tnany  thottsands  of 
dollars,  all  through  "dead  rock,"  in  the  hopes  of  cross-cut- 
ting a  certain  ore  body  that  had  proved  rich  near  the  sur- 
face. At  last  it  was  given  up,  and  subsequently  a  short 
cross-cut  was  made  from  it,  and  the  original  vein  was  found 
only  a  few  feet  from  the  tunnel,  which  had  been  running 
parallel  with  it  all  the  time.  The  cause  of  the  mistake 
was  an  unforeseen  fault  in  the  vein  that  had  shifted  its 
dip  much  further  on  one  side  than  had  been  calculated 
upon. 


CHAPTER   IX. 


GOLD   I'l.AChRS. 

PROSPECTINC     FOk     I'LACKR    C.OU^    AND    C.Ol.Vt    VF.INS. 

Having  given  in  preceding  chapters  a  sketch  of  veins 
and  ore  deposits  in  the  rocks,  it  follows  in  order  to  speak 
of  gold  placers,  because  these  arc  derived  from  the  former 
by  the  agencies  of  water,  either  in  the  form  of  glaciers  of 
old,  or  of  ancient  or  modern  streams. 


ti 


Plate  LXIV. 

Open  Placer  Grounds  in  Canyon. 

The  glaciers  in  olden  times  heavily  mined  the  rocks  and 
the  veins,  by  cutting  broad  gashes  through  them,  thus 
originating  the  canyons.  In  this  way  millions  of  tons  of 
rock  were  mined,  together  with  the  gold-bearing  veins  in 


111 


I  12 


them,  and  also  the  precious  metals  minutely  diffused  and 
scattered  throughout  their  masses. 

After  the  glaciers,  the  rivers  took  up  the  work,  deepened 
the  canyons,  broke  up  the  boulders  and  sorted  them,  setting 
free  the  gold  and  other  metals  they  contained,  and  again 
sifted  and  sorted  them  and  deposited  them  along  their 
banks  and  in  their  beds. 

Of  the  various  metals  thus  handled  by  nature's  jigging 
process,  many  were  dissolved  and  destroyed  by  various 
acids  in  the  waters,  and  by  acids  of  vegetation  and  iron 
salts  percolating  through  the  placer  dumps  after  they  had 
been  laid  down.  So  with  the  exception  of  a  few  very  hard 
minerals,  such  as  magnetite,  diamonds,  garnets,  rubies, 


Plate  LXV. 

Section  in  Gold  Placer. 


etc..  little  remained  in  the  placer  but  the  imperishable 
gold,  and  even  that  appears  to  have  been  refined  of  its 
alloy  of  silver  which  it  contained  in  the  original  vein,  for 
placer  gold  is  generally  much  purer  and  more  valuable 
than  that  in  the  original  vein. 

In  some  cases,  too,  the  fine  gold  disseminated  through 
the  placer  appears  to  have  been  acted  upon  by  certain 
salts,  such  as  the  persalts  of  iron,  and  concentrated  and 
amalgamated  into  large  nuggets.  Some  contend,  however, 
that  these  nuggets  are  only  waterworn  pebbles  of  gold, 
brought  direct  from  the  vein,  the  result  perhaps  of  con- 
centration there  of  the  contents  of  large  masses  of  gold- 
bearing  pyrites;  it  is  to  be  noted,  however,  that  whilst 
gold-bearing  nuggets  of  various  sizes  are  to  be  found,  not 


»«3 

lUK  «iinin»)nly  in  ifold  placers,  ihcy  arc  very  rarely  lounU  in 
j;olci  veins. 

With  the  gold  in  placers  is  commonly  found  what  is 
called  "  black  sand,"  which  is  composed  of  grains  or  peb- 
bles of  magnetic  iron  ore.  relics  of  the  old  gold-bearing 
pyrites  chemically  changed.  Being  near  in  gravity  to 
gold,  and  originally  associated  with  it,  the  two  are  gener- 
ally found  together  in  a  placer,  and  a  prospector  in  sur- 
veying a  bank  of  placer-material  made  up  of  sand,  pebbles 
and  boulders,  generally  looks  for  a  streak  ot  "  black  sand" 
as  a  likely  place  for  gold.  Also  by  reason  oi  the  gravity 
of  gold  he  is  inclined  to  look  for  it  more  down  on  bed- 
rock than  in  the  upper  loojier  strata. 

Ancient  river  beefs  as  well  as  those  of"  modern  rivers  may 
be  found  gold-bearing,  rivers  that  have  long  ceased  to 
flow,  by  reason  perhaps  of  change  in  the  configuration  of 
the  country.  In  California  and  Australia  many  of  these 
ancient  gold-bearing  river-beds  have,  at  a  period  not  long 
distant,  been  deluged  and  covered  by  lava,  and  the  gold  is 
extracted  by  tunnelling  beneath  the  lava-sheet  or  by  shaft- 
ing down  through  it  to  the  gravel  below.  These  are  called 
deep  leads,  whilst  the  ordinal  y  uncovered  gravels  are  called 
"shallow  placers." 

Almost  anywhere  along  ancient  or  modern  water  courses 
not  far  from  mountains,  a  prospector  by  panning  can  get 
colors  of  gold  even  on  the  pebbly  "  wash"  covering  the  sur- 
faces of  large  portions  of  our  plains,  or  even  on  the  tops  of 
table  lands  that  once  were  plains,  over  which  broad  rivers 
and  glaciers  and  large  bodies  of  water  distributed  their 
debris,  but  as  a  rule  it  will  only  pay  to  work  where  the 
"  wash"  or  "  drift"  or  "  alluvial"  matter  is  plentiful  and 
thick,  and  more  than  this,  only  where  water  is  accessible 
to  the  work. 

PROSPECTING. 


A  prospector  hunting  for  a  gold  placer  follows  up  the 
water  channels  in  which  he  finds  specimens  of  all  the  rocks 
in  the  neighborhood.  In  Australia,  the  prospector  looks 
amongst  these  to  find  samples  of  granitic,  porphyritic  and 
quartzose  rocks  or  clay-slate  as  likely  signs,  ana  also  pieces 
of  quartz  honey-combed  and  rusty,  which  we  have  de- 
8 


114 


I  ; 


scribed  before  as  "  float  or  blossom.  "  Plenty  of  broken  up 
quartz  he  considers  a  good  sign,  but  very  pure,  hard,  dull 
white  quartz  is  generally  considered  as  "  hungry"  or  "  bar- 
ren;" the  size  of  the  fragments  denotes  his  nearness  or 
otherwise  to  the  reef,  i.e.,  the  vein. 

A  prospector  examines  closely  the  fine  sandy  matter  of 
the  stream  bed,  especially  where  eddies  and  backwater  have 
Deen  formed.  A  likely  deposit  should  be  scraped  up,  even 
down  into  every  crevice  and  depression  in  the  bed  rock 
or  solid  rock  bottom  over  which  the  river,  modern  or 
ancient,  has  worn  its  channel.  This  material  should  be 
panned.  Gold,  too,  is  often  found  on  points  and  slopes  of 
the  bed  rock  as  well  as  in  the  deepest  portion.     Nuggets 


\>    t0 


Plate  LXVl. 

Shallow  Placer— Gold  Sand  in  Potholes  A,  A  and  Beluw  a   Hard  "  Hat      I?. 


found  on  high  reefs  above  the  level  of  the  stream,  imply 
that  their  weight  enabled  them  to  remain  in  their  position, 
during  the  deeper  erosion  of  the  neighboring  streams,  and 
that  the  original  vein  from  which  they  came  is  not  far 
off.  As  a  rule,  large  nuggets  and  coarse  gold  are  found 
much  nearer  to  the  source  whence  they  came,  than  fine  or 
"  flour"  gold,  which  is  often  carried  to  unlimited  distances 
away  out  on  the  plains. 

The  character  of  quartz  veins  and  of  their  enclosing 
rocks  in  the  immediate  viciniiy,  decides  the  character,  too, 
of  gravels  derived  from  them,  hence  sometimes  a  peculiar 
pebble  may  be  traced  up  to  the  peculiar  rock  whence  it 
came,  and  the  gold  vein  be  found  near  it  in  place. 

It  has  been  observed  that  "  Xesidis"  following  the  course 


"5 


or  lines  of  a  gold-bearing  reef,  maintain  a  more  continuous 
yield  than  those  crossin^t^  a  number  of  gold  reefs  at  intervals. 

Gold  occurs  in  pockets  and  "  shoots"  at  intervals,  with 
barren  portions  between,  which  accounts  for  what  we  have 
stated  above.  In  a  country  where  the  gold  quartz  veins 
are  small,  though  rich  at  wide  intervals,  the  gravels  will 
also  be  small. 

In  very  deep  ground  where  the  "  wash"  is  very  heavy  a 
series  of  borings  or  even  shafts  are  made  to  test  the  quality 
of  the  bank.  The  following  points  have  been  observed  as 
worthy  of  note  in  prospecting  for  gold  placers. 

r.  Streams  crossing  the  lamina  or  stratification  planes 
(»f  gold  reefs  at  right  angles  are  likely  to  be  richest. 

2.  Gold  is  rarely  found  plentiful  where  there  are  indica- 
tions that  the  current  was  strong,  but  rather  in  the  lee 
under  projecting  points  of  rock,  where  beaches  are  usually 
formed  and  the  water  was  slack. 

3.  Gold  in  streams  is  deposited  in  crevices  of  the  "  bed 
rock,"  which  should  be  laid  as  dry  as  possible  and  picked 
up  to  such  depths  as  the  sand  descends  between  the 
laminations. 

4.  Terraces  are  shelf-like  excavations  and  deposits  upon 
hill  slopes  above  valleys,  and  are  the  remains  of  old  glacier 
or  river  beds.  The  prospector  should  discover  the  inlet 
and  outlet  of  the  terrace  and  examine  the  gravel.  The 
"  wash"  sometimes  contains  gold  in  layers  one  above  the 
other. 

5.  Whilst  working  up  stream  a<:tention  should  be  paid  to 
the  banks  on  each  side  where  sections  are  exposed  so  that 
no  outcropping  vein  be  overlooked. 

6.  Alluvial  gold  should  if  possible  be  traced  to  its  source 
whence  the  "  float"  came.  When  the  gold  is  large  and 
plentiful  and  the  boulders  large  and  angular  the  reef  is 
likely  not  far  distant. 

7.  Sometimes  there  is  a  distinct  peculiar  feature  in  all 
the  veins  of  a  district,  such  as  a  peculiar  band  of  a  definite 
color. 

8.  Coarse  alluvial  gold  is  not  always  incompatible  with 
fine  reef  gold  as  a  source,  because  the  reef  gold  may  be  so 
fine  in  general  as  to  lend  itself  to  very  wide  distribution 
when  once  it  is  liberated,  while  the  rarer  coarse  grains 
would  not  be  transported  far. 


ii6 


9.  Alluvial  placers  are  richest  where  the  current  of  the 
stream  is  interrupted  by  diminution  in  fall,  by  sudden 
change  of  direction,  or  by  entrance  of  a  tributary,  also  by 
reefs,  bars,  eddies,  etc.  Absolute  richness  depends  upon 
local  circumstances  and  the  size  and  weight  of  floated 
masses. 


i  ii 


Plate  LXVII. 

Sliallow  Placer— Gold  Sand  Behind  Bar  on  One  Side  of  Creek. 

10.  Creases,  holes  and  fissures  of  bed-rock  over  which 
the  stream  passed  are  favorite  places. 

1 1.  The  lowest  layers  of  each  separate  period  of  deposi- 
tion are  the  richest. 

Sometimes  several  different  periods  of  deposition  have 
succeeded  each  other. 

1 2.  The  courses  of  present  streams  and  of  ancient  chan- 
nels are  placers. 

"  Loaming"  is  a  form  of  prospecting.  It  is  preliminary 
to  such  prospecting  as  cutting  experimental  trenches,  or 
sinking  trial  shafts  or  boring.  It  consists  in  washing  sur- 
face prospects  from  the  bases  and  slopes  of  the  ranges, 
until  specks  of  gold,  or  specimens  are  found  to  be  obtain- 
able with  tolerable  frequency,  within  certain  limits.  The 
prospector  then  proceeds  to  trace  the  gold  up  hill  to  its 
source,  narrowing  the  limits  of  his  work  as  by  patient 
search  he  approaches  the  vein,  whence  the  gold  has  been 
derived.  When  he  can  obtain  surface  prospects  of  gold 
up  to  a  certain  point,  or  line,  but  no  farther,  he  then  pro- 
ceeds by  means  of  trenching  to  search  for  the  gold  vein. 
The  prospector  has  often  to  work  along  a  steep  scrubby 
mountain  side,  selecting  his  prospects,  numbering  them, 


i  f 


117 

and  placing  samples  in  .lis  "  loam  bapf."  If  he  discovers 
prospects  of  gold,  he  finds  his  way  back  to  the  spots  the 
samples  were  taken  from,  so  as  to  continue  his  up-hill 
search,  and  trace  the  gold  to  its  source  or  vein.  Some- 
times there  is  no  indication  of  a  vein,  soil  and  bush<;s  and 
debris  covering  its  out-crop,  but  by  loaming,  the  prospector 
ascertains  its  position,  so  as  to  expose  it  by  a  trench  not 
many  feet,  in  length. 

We  remember  an  ingenious  way  in  which  a  valuable  and 
long  sought  for  vein  was  at  last  discovered.  Prospectors 
liad  long  found  very  rich  "  float"  at  the  base  of  a  hill  whose 
surface  was  so  deeply  covered  with  loose  debris  that  no 
trace  of  the  vein  could  be  found.  A  prospector  found  a 
small  lake  on  top  of  this  hill,  and  conceived  the  idea  of 
cutting  a  trench  from  this  body  of  water  to  the  edge  of 
the  hill,  and  by  damming  up  the  trench,  and  then  suddenly 
letting  out  the  water  to  full  force,  it  cut  a  deep  trench 
through  the  loose  debris  down  to  bed  rock  and  the  vein  was 
discovered.     This  process  is  called  "  booming." 

The  cleava[^e  of  quartz  is  said  to  be  freer,  sharper  and 
better  defined,  in  gold-bearing  quartz  than  in  that  which 
is  barren.  Pyrite  is  a  good  indication.  A  soft,  fatty  clay 
or  gouge  often  flanks  the  vein  in  its  gold-bearing  portions. 

The  mountain  spurs  should  first  receive  attention  for 
veins;  if  the  quartz  is  hard,  it  stands  up,  if  soft,  as  it  more 
commonly  is,  it  will  leave  a  streak-like  depression.  On 
finding  such,  the  prospector  should  first  wash  out  some  of 
the  decaying  rock.  If  only  a  trace  of  gold  is  found  in  the 
quartz,  there  is  probably  a  gold  vein  in  the  neighborhood, 
and  trenches  should  be  dug  and  exploration  systematically 
followed  up.  Gold  is  generally  near  one  wall  of  a  vein, 
seldom  all  through  the  stone.  Quartz  gold  occurs  in 
"  shoots"  with  barren  spaces. 

Before  setting  a  valuation  on  a  discovery,  the  facilities 
for  working  the  mine,  such  as  we  have  alluded  to,  should 
be  considered.  Placer  mines  as  well  as  other  mines  are 
often  supposed  to  be  "  worked  out."  These  are  sometimes 
well  worth  investigating  and  examining  by  cross-cuts  or 
other  means.  Sometimes  it  happens  that  more  gold  is  ob- 
tained from  "  leader"  veins  that  had  been  overlooked,  than 
from  the  main  worked  vein. 

Quite  commonly,  especially  in  the  lower  part  of  a  placer, 


ii8 


I 


the  pebbles  and  sand  are  firmly  cemented  together  into  a 
coarse  conglomerate  by  inliltration  of  iron  oxide  and  clay. 
This  may  consolidate  into  a  false-bottom  and  not  be  true 
"  bed  rock."  Generally  two  or  three  such  false-bottoms, 
with  intervening  strata  of  greater  richness,  alternate  with 
barren  ones.  So,  many  old  diggings,  thus  supposed  to 
have  been  exhausted,  ni.;y  be  worked  again,  the  true  bot- 
tom not  having  been  reached.  These  conglomerate  bot- 
toms may  lie  just  upon  bed-rock,  with  a  white  clay  rich  in 
gold  beneath  them.  Gold  occurs  also  in  the  conglomerate 
and  must  be  stamped  out. 

Modern  rivers  frequently  cross  in  their  course  old  river 
courses,  and  redistribute  their  golden  sands. 

Placers  are  richer  in  their  richer  parts,  tha.i  the  veins 
from  which  their  gold  was  derived. 

When  shallow  placers  are  due  to  the  wearing  down  of 
quartz  veins,  no  placer  will  be  found  above  these  veins, 
or  above  the  point  where  the  vein  crosses  the  placer.  In 
the  Sierra  Nevada  there  is  but  little  alluvium,  the  gold 
comes  from  veins  near  by. 

Gold  placers  may  sometimes  occur  below  silver  mines. 
Thus  the  Comstock  vein  was  discovered  by  following  up 
placer  gold  to  its  source.  This  vein  has  produced  a  gold- 
bearing  silver-ore,  the  silver  rapidly  disappearing  and 
leaving  the  geld  behind. 

EXAMPLE    OF    A    PLACER. 

In  Ballarat,  Australia,  the  '*  wash-dirt"  runs  in  a  series  of 
"  leads" of  varying  width,  starting  from  the  same  point,  and 
trending  in  different  directions  towards  the  "  deep  leads.' 
The  "  reef  wash"  is  about  loo  feet  deep,  the  "  pay  dirt"  5 
feet.  The  barren  drift  wash  overlying  the  "  pay  dirt"  is 
of  black  clay.  The  reef  itself  is  of  green  slate,  the  bed- 
rock is  sandstone.  Gold  lies  sometimes  on  thin  layers  of 
sand  or  "  pipe  clay"  on  the  surface  of  the  "  bed-rock,"  more 
often  in  crevices  of  the  bed-rock  itself,  which  is  more  or 
".ess  rotten.  This  bed-rock  is  broken  up  for  some  12  to  20 
inches  and  the  gold  is  found  in  "pot-holes"  in  it  15  to  18 
inches  in  diameter  and  6  to  10.  inches  deep,  cut  out  of  the 
solid  rock.  The  alluvial  gold  is  found  chiefly  in  bed-rock 
of  slate,  dipping  90  degrees.  Some  of  these  slates  are  soft 
and  rotten,  tithers  are  indurated.     On  the  soft  rock  only  is 


119 

the  gold  found.  Nuggets  are  found  in  the  soft  clay  lying 
on  "bed-rock."  Slate  forms  natural  "  riffles"  for  catching 
the  gold. 

Deep  pools  under  waterfalls  in  gold-bearing  streams 
rarely  carry  much  gold.  So  in  rivers,  gold  is  found  in 
"  bars"  or  points  rather  than  in  deep  pools  or  bends. 


CHAPTER    X. 


DEEP     LEADS. 

A  "  deep  lead"  lies  deep  below  the  surface,  often  covered 
by  beds  of  lava,  especially  in  California.  These  lava 
beds  may  be  many  in  number,  and  hundreds  of  feet  in 
thickness.     The  "  deep  lead"  is  an  ancient  river  bed. 

In  the  Sierra  Nevada  the  gold  is  derived  from  metamor- 
phic  crystalline  rocks  of  the  range,  partly  from  quartz  veins 
in  the  slates,  and  partly  from  gold  distributed  in  minute 
quantities  all  through  the  metamorphic  rocks.  The  quartz 
veins  lie  between  the  planes  of  stratification  of  the  slates, 
also  in  irregular  bunches  and  lenticular  masses  of  limited 
extent.  In  many  localities,  the  rocks  are  penetrated  in 
every  direction  by  little  irregular  quartz  veinlets,  which 
often  carry  gold,  and  in  spots  are  extremely  rich,  even 
where  the  quartz  vein  is  only  an  inch  thick.  In  some  Cali- 
fornia districts,  wherever  a  basalt  capping  exists,  the  drift 
beneath  it  is  auriferous. 

In  California  the  modes  of  occurrence  of  auriferous  gravel 
deposits  are  various. 

"  Sometimes  they  exist  in  well-defined  ancient  river-beds 
under  a  capping  of  basalt  which  has  filled  the  channels  of 
the  rivers  in  past  ages.  Again,  they  appear  in  isolated 
mounds  or  hillocks,  evidently  the  remains  of  such  channels, 
which,  being  unprotected  by  a  covering  of  lava,  have  been 
broken  up  by  the  action  of  the  elements,  also  in  basins  or 
flats  whch  have  received  the  wash  of  these  disintegrating 
rivers,  also  in  low,  rolling  hills  neai  the  base  of  the  Sier- 
ras, and  beyond  the  reach  of  the  lava-flows."  One  of  the 
most  remarkable  and  important  gold  leads  is  that  beneath 
Table  Mountain  in  Tuolumne  County.  "  The  waters  per- 
colating through  these  lava-flows  and  reaching  the  gravels 


120 

beneath,  are  charged  with  alkali  from  the  lava.  These 
alkaline  waters  are  charged  with  silica  in  solution  from 
the  same  source.  Hence  the  fossil  drift-wood  of  these 
ancient  rivers  has  all  been  silicified  by  these  silicious 
waters.  The  gravels  are  also  cemented  by  the  same  ma- 
terial. These  percolating  waters  also  contained  iron,  for 
iron  pyrites  is  found  in  contact  with  the  silicified  wooc's. 
In  this  iron-cement,  gold  is  found  in  rounded  grains  and  m 
minute  crystals,  and  threads  deposited  by  a  solution  of 
sulphate  of  iron  at  the  moment  of  the  reduction  of  the  latter 
to  a  sulphide," 

BABnr 


Plaik   LXVIII. 

Deep  Placer,  Table  Mountain,  Cul.— A  A,  Ancient  River  Channel,  with 
Gold-bearing  Gravel ;  B  B,  Sandstones  and  Shales  with  PoFsil  Bones  and 
Silicified  Wood. 


The  dead  rivers  of  California  are  on  the  west  slopes  of 
the  Sierra  Nevada,  from  500  to  7,000  feet  above  sea-level. 
The  largest  and  richest  lead  is  the  "  Big  Blue  Lead,"  traced 
65  miles  and  even  1 10  miles.  It  is  parallel  with  the  main 
divide  of  the  Sierra  Nevada.  The  live  modern  rivers  run 
at  right  angles  to  it,  cutting  canyons  1,500  to  3,000  feet 
deep.  The  "  Blue  Lead"  runs  across  these  ridges  from  200 
to  1,000  feet  below  their  summit.  The  lead  was  discovered 
by  following  up  surface  washings.  Miners  found  that  the 
modern  streams  were  richly  gold-bearing  up  to  a  certain 
point,  increasing  as  this  point  was  neared  but  ceasing  when 
It  was  passed.  These  parts  were  in  the  line  of  the  different 
streams,  and  by  following  up  indications,  the  lead  was 
eventually  struck  on  several  sections  and  tunnelled  on. 
The  deposit  is  300  feet  deep,  composed  of  gravel,  boulders, 
clay,  and  sand,  on  strata  distinguished  by  degrees  of  fine- 


T3I 

nes5>,  by  the  character  of  the  rocks,  and  the  amount  of  {fold, 
also  by  colors,  the  prevailing  color  being  a  bhiegray. 
(iold  is  coarser  near  the  bottom,  and  contains  a  greater 
alloy  of  silver.  The  silver  in  the  gold  in  the  upper  strata 
has  been  eaten  out  by  sulphurous  acid  resulting  from  de- 
composition of  iron  pyrites.  The  whole  deposit  is  like  that 
in  existing  rivers,  showing  banks,  bars,  eddies,  falls,  rapids 
and  riffles.  There  is  much  gold  in  the  eddies,  and  but  little 
in  the  rapids.  The  space  between  the  boulders  is  filled 
with  sand  and  contains  gold,  the  bed-rock  is  slate. 

Where  dead-rivers  meet,  the  "  wash"  is  generally  rich. 
Where  a  lead  becomes  very  narrow,  dips  fast,  and  is  in- 
closed between  steep  walls,  the  gold  will  be  very  sparingly 
distributed  in  holes  and  behind  ridges  and  will  be  coarse 
in  size. 

Very  large  and  abundant  boulders  in  gold-bearing  stream 
beds  are  often  a  serious  obstacle  in  getting  out  the  gold, 
from  the  difficulty  of  handling  them.  More  than  one  placer 
has  been  abandoned  from  this  cause  alone. 


HYDRAULICS. 

Placer  banks  are  worked  on  a  large  scale  by  "  Giant  noz- 
zles" or  Hydraulics.  Before  commencing  such  work  the 
total  depth  of  the  placer  deposit  should  be  examined  and 
ascertained,  and  the  richness  of  the  strata  throughout 
tested.  Shafts  should  be  sunk  here  and  there  to  bed-rock 
for  this  purpose,  and  topograhical  surveys  made  to  ascer- 
tain what  fall  and  head  of  water  can  be  obtained,  and  what 
outlet  also  for  the  tailings,  as  the  latter  would  soon  choke 
up  the  work ;  the  ground  sometimes  may  be  too  flat  to  dis- 
l)ose  of  the  tailings  by  stream-power.  The  choking  of  out- 
lets is  a  fertile  source  of  abandoning  placers. 

Beach  Mining. — "  The  beach  sands  of  the  Pacific  and  else- 
where contain  minute  scales  of  gold  and  sometimes  plati- 
num, together  with  a  great  deal  of  magnetic  iron  ore. 
Winds,  tides,  and  surf  act  as  natural  concentrators  or  sepa- 
rators in  parting  the  light  and  useless  material  from  the 
heavier.  Wind  drives  heavy  swells  on  the  beach  at  high 
tide  together  with  sandy  matter.  At  ebb  of  tide,  the  surf 
lashes  the  beach  and  carries  back  light  portions  of  the  mass 
with  the  undertow,  leaving  some  iron  sand,  gold  and  plati- 


I  y 


i:  3 


; 


num,  whose  weight  enables  them  to  hold  their  place.  At 
low  water,  miners  go  down  on  the  beach,  scrape  up  the  iron 
sand,  which  is  generally  left  in  thin  layers,  stacking  it  back 
from  reach  of  the  surf,  and  subsequently  washing  out  the 
gold."  In  some  beaches  much  of  this  sand  contains  titanif- 
erous  iron  ore,  and  if  attempts  are  made  to  use  certain  pro- 
cesses to  save  the  finer  gold  the  character  of  the  iron  may 
be  a  formidable  obstacle. 

EXAMPLE    OF    COLORADO    PLACER    GOLD    MINES. 

California  gulch,  the  site  of  the  present  Leadville,  fur- 
nished a  great  amount  of  gold  in  the  early  days  till  the  dis- 
covery of  the  lead-silver  deposits  in  place.  This  discov- 
ery, also,  was  due  to  placer  mining.  Whilst  examining 
the  gravel  in  the  gulch,  Mr.  Wood,  an  intelligent  prospec- 
tor, was  struck  by  the  appearance  of  what  the  miners  called 
"heavy  rock,"  some  of  which  he  assayed.  His  specimens 
yielded  27  per  cent,  lead  and  1 5  ounces  silver  to  the  ton. 
He  put  prospectors  to  work  to  find  the  croppings  of  the  ore 
deposits,  and  in  June,  1874,  the  first  "carbonates  in  place" 
were  found  on  Dome  Hill.  This  was  practically  the  be- 
ginning of  Leadville.  It  is  said  that  upwards  of  2,000,000 
dollars  worth  of  gold  was  taken  out  of  this  gulch  in  one 
summer  before  the  mines  in  place  were  discovered  or 
opened  up. 

It  is  noticeable  that  California  gulch  alone  furnished 
almost  all  this  placer  gold,  whilst  Iowa  and  Evans  gulches 
adjoining  it  on  either  side  and  carved  out  of  the  same  se- 
ries of  rocks,  yielded  little  or  nothing.  Why  should  the 
smaller  gulch  contain  exceptionally  rich  gravels  and  its 
neighbors  be  barren? 

The  richest  portions  of  California  gulch  were  found  at 
bends  in  the  course  of  the  gulch.  In  one  place  near  Oro 
in  the  narrow  bed  of  the  gulch,  a  gold-bearing  cement  was 
found  containing  hydrated  oxide  of  iron,  below  the  gravel, 
yielding  an  ounce  of  gold  to  the  ton.  The  gulch-gold  was 
worth  $19  per  ounce  whilst  that  from  the  mines  in  place 
only  $15.  The  Printer  Boy  porphyry  containing  actual 
gold  veins  in  place  may  have  been  the  source  of  some  of 
the  gold  in  the  gravels,  together  with  the  oxide  of  iron 
resulting  from  the  decomposition  of  pyrites  in  the  pyritif- 
erous  porphyry  as  a  cementing  material.     Also  the  "  Weber- 


»«3 

grit"  sandstones  at  the  head  of  the  jn^lch  have  been  found 
to  carry  small  gold  veins,  and  from  their  abrasion  also 
gold-bearing  gravels  would  have  been  carried  down  the 
gulch.  Also  of  late  the  rich  gold  deposits  of  Breece  Hill 
at  the  Ibex  and  Little  Johnnie  mines  have  been  found. 

"  It  is  doubtful,"  says  Mr.  Emmons,  "  whether  in  general, 
all  or  even  the  greater  part  of  the  gold  contained  in  placer 
gravels  is  derived  from  the  abrasion  of  actual  gold  veins. 
Traces  of  gold  may  be  found  in  a  very  large  proportion  of 
the  massive  rocks  which  form  the  earth's  crust.  Gold  veins 
are  concentrations  of  this  mineral  in  sufficient  quantity  to 
attract  attention  and  yield  a  profit.  But  doubtless  there 
are  a  vast  amount  of  smaller  concentrations  which  may 
escape  notice.  As  the  rock  disintegrates  and  is  worn  away 
Ijy  atmospheric  agencies,  the  gold  from  these  smaller  de- 
posits as  well  as  from  the  larger  is  set  free  from  its  inclos- 
ing rock  and  subjected  to  the  concentrating  action  of  moun- 
tain streams. 

"  Placer  deposits  are  the  results  of  nature's  vast  sluicing 
processes.  To  bring  them  into  the  condition  in  which  they 
may  be  made  available  by  man,  requires  not  only  the  gold- 
bearing  rock,  which  her  agencies  may  grind  up  into  sand 
and  gravel,  but  the  sifting  power  of  rapid  streams,  which 
may  carry  down  the  lighter  and  coarser  material,  and  a 
suitable  channel  in  which  the  heavier  particles  may  lodge, 
as  in  the  riffles  of  a  sluice  box.  All  mountain  gravels,  all 
sands  of  rivers  coming  from  the  mountains,  contain  a  cer- 
tain amount  of  gold,  but  it  is  only  under  peculiarly  favor- 
able conditions  that  the  gold  is  so  concentrated  as  to  render 
the  gravel  remunerative. 

"  Among  the  most  favorable  of  these  conditions  is  a  com- 
paratively narrow  channel  having  a  hard  and  compact  bed- 
rock, and  ridges  or  bends  in  its  course,  which  by  causing 
a  partial  arrest  in  the  rapidity  of  the  current  shall  allow 
the  heavier  particles  of  gold  to  settle  to  the  bottom,  and 
hold  them  there  when  once  they  have  settled. 

"  From  this  point  of  view  there  is  a  very  evident  reason 
why  California  gulch  should  have  furnished  rich  placers, 
and  why  the  gold  which  may  exist  in  Iowa  and  Evans 
gulches  should  not  yet  have  been  extracted  even  though 
the  detrital  material  which  has  been  carried  down  the  gulch 
should  originally  have  been  equally  rich  in  gold. 


M.. 


i  i 


^' 


194 


"  California  gulch  is  a  valley  of  erosion,  formed  entirely 
by  the  action  of  running  water,  and  since  the  glacial  period. 
It  has  therefore  a  bottom  or  bed  of  hard  rock.  Its  trans- 
verse section  is  V  shaped  and  therefore  favorable  for  the 
concentration  of  heavy  particles  at  its  bottom.  When  com- 
paratively full  of  water,  its  numerous  bends  formed  eddies 
in  the  down-flowing  currents,  and  allowed  a  longer  time  at 
these  points  for  the  settling  of  the  surface  particles,  and 
as  it  cuts  across  many  different  formations  m  its  course, 
its  bed  must  have  transverse  ridges,  which  have  caught 
some  of  the  gold  and  prevented  it  from  being  carried 
farther  down  the  stream. 

"  Evans  and  Iowa  gulches  on  the  other  hand  are  glacier- 
carved  valleys.  Their  courses  are  straight,  their  bottoms 
broad  and  comparatively  smooth.  The  glacial  moraine 
material  with  which  they  are  largely  filled  has  not  been 
subjected  to  the  sifting  or  jigging  process  to  which  gravel 
is  subjected  in  the  bed  of  a  stream.  The  lower  part  of 
their  present  beds  is  cut,  not  out  of  rock,  but  out  of  the 
loose  gravelly  formation  of  the  'Lake  beds.'  This  later 
bed,  along  which  the  material  brought  down  by  post-glacial 
erosion  has  been  carried,  has  not  a  sufficiently  hard  and 
permanent  bed-rock  to  allow  of  the  concentration  of  gold 
on  its  surface." 


A        A    AND    FAIRPLAV     PLACERS,    SOUTH    PARK. 

Along  the  banks  of  the  Platte  river  are  enormous  masses 
of  glacial  morainal  matter  consisting  of  boulders  and  sand 
brought  down  partly  and  principally  from  Mount  Lincoln 
and  receiving  contributions  from  side  glaciers  of  the  Mos- 
quito range.  This  material  forms  undulating  banks  on 
either  side  of  the  river.  This  placer  "  wash,"  from  50  to 
100  feet  thick,  is  worked  for  gold  principally  at  Alma  and 
Fairplay. 

At  Alma  the  heavy  bank  of  "  wash"  is  mined  by  the  giant 
nozzle.  The  banks  are  also  cut  back  into  blocks  of  ground, 
by  water  from  a  flume,  which  is  let  out  at  intervals  along 
the  bank  above ;  at  each  place  it  cuts  a  narrow  ravine  in 
the  loose  debris  and  at  the  same  time  makes  the  banks 
easier  to  be  attacked  by  the  water  of  the  giant  nozzles, 
which  rapidly  undermine  them.     The  water  and  sand  from 


12< 

these  streams  run  down  into  the  shiices.  whose  ht)ttoms  are 
paved  with  discs  of  wood,  forming  "  riffles'"  to  catch  the 
gold,  whilst  the  lighter  sand  is  carried  onward  by  t"^e 
stream.  In  their  "  clean  up"  in  the  stream  bed.  they  not 
only  wash  down  to  bed-rock,  but  after  hunting  with  their 
knives  in  every  crack  and  crevice  of  the  latter,  they  dig 
it  up  for  a  foot  or  two,  and  further  examine  it.  The  rock 
is  a  jointed  sandstone. 

Quicksilver  is  thrown  into  the  sluices,  to  collect  the 
finer  gold  which  is  afterwards  retorted.  Whilst  gold  is 
found  all  through  this  bank  of  "  wash"  from  "  grass  roots" 
down  to  bed-rock,  the  greatest  quantity  of  gold  and  largest 
nuggets  are  found  at  "  bed-rock"  or  in  its  interstices. 

The  .source  of  some  of  this  gold  may  be  a  series  of  large, 
but  not  very  productive  quartz  veins  iu  granite,  near  Mount 
Lincoln,  whence  the  main  glacier  originated.  It  is  also 
probable  that  a  good  deal  of  the  gold  came,  as  said  before, 
from  the  breaking  up  of  the  various  rocks  in  which  it  was 
disseminated,  more  especially  the  porphyries  and  crystalline 
rocks. 

In  the  winter,  owing  to  freezing  of  the  water  supply,  the 
work  has  to  be  discontinued  till  the  following  spring. 


CHAPTER  XI. 

MINING   REGIONS  SHOWING    EXAMPLES  OF    ORE 

DEPOSITS. 


FISSURE   VEINS   IN    GRANITIC    ROCKS. 

Having  described  in  previous  chapters  the  nature  of 
veins,  ore  deposits,  etc.,  and  how  to  prospect  them,  it 
will  be  of  interest  as  well  as  profit  to  the  prospector,  to 
learn  something  of  the  mines  and  mining  regions  them- 
selves. For  this  purpose  we  propose  giving  a  sketch  of 
some  of  the  leading  mining  regions  of  Colorado  and  the 
West,  as  instructive  illustrations  and  examples  of  what  we 
have  written  in  previous  chapters.  As  we  said  in  our 
advice  as  to  the  education  of  a  prospector,  the  best  educa- 
tion for  him  is  to  go  to,  and  spend  as  much  time  as  he  can 
in,  the  mines  and  mining  regions  themselves. 


126 

Wc  will  take  first  the  regions  iharactcrized  by  Jissure 
veins.  These  veins  are  in  the  granitic  and  igr^euiis  districts 
of  Colorado.  In  the  granitic  ranges,  the  mining  districts 
of  HouUkr  county,  Gilpin  and  Clear  Creek,  are  the  most 
noted,  the  jirincipal  mining  towns  being  Boulder,  Jimtown, 
Georgetown,  and  Central  and  Idaho  Sjirings. 


ROUI.DF.R    MINFS. 

The  geological  features  of  Boulder  consist  in  a  series  of 
ridges  or  hogbacks  rising  up  from  the  prairie  and  flanking 
the  granite  mountains.  These  represent  Mesozoic  strata 
consisting  of  sandstones,  limestones  and  shales,  containing 
beds  of  coal  and  other  economic  products,  but  no  precious 
metal.  Volcanic  action  has  occurred  in  their  vicinity  as 
shown  by  a  large  dyke  of  basalt  at  Valmont.  These  hog- 
backs, so  universally  present,  flanking  the  granite  moun- 
tains, are,  in  Colorado,  destitute  of  precious  ores.  Inside 
of  and  west  of  these  is  the  Archaean  granitic  front  range, 
consisting  of  heavily  bedded  granite-gneiss,  profusely 
traversed  by  veins  of  *'  pegmatite"  or  very  coarse  sparry 
granite,  consisting  of  white  feldspar  and  quartz,  with  very 
little  mica,  and  from  a  few  inches  to  40  or  50 feet  in  width; 
with  these  also  occur  some  dykes  of  eruptive  rock,  some  of 
it  a  dark  black  rock  like  basalt,  called  "diabase";  others 
are  lighter  colored  quartz  porphyries  and  diorites.  In  the 
telluride  belt,  whilst  pegmatite  veins  are  abundant,  erup- 
tive rocks  are  scarce,  but  west  of  the  telluride  belt,  which 
is  more  or  less  confined  to  a  special  area  underlying  the 
Magnolia,  Sugar  Loaf,  Gold  Hill  and  Central  districts, 
enormous  masses  of  eruptive  rock  are  foun^.  but  no  tellu- 
rides.  In  the  non-telluride  districts,  such  as  Caribou, 
Weird  and  Jimtown,  rich  silver  ores  are  found  associated 
with  galena,  gray  copper,  etc.,  and  gold  ores  associated 
with  copper  and  iron  pyrites.  Thus  there  are  two  or 
three  distinct  belts  in  the  region,  a  telluride  gold  belt,  and 
a  silver  belt,  and  a  gold  pyrites  belt.  It  is  noticed  that 
the  entire  region  has  been  locally  disturbed  by  volcanic 
forces,  and  volcanic  rocks  abound ;  outside  of  this  disturbed 
region  there  are  no  mines  for  a  long  distance. 

The  Boulder  mines  are  celebrated  for  the  occurrence  of 
telluride  minerals,  some  of  the  richest  and  rarest  ores  oc- 


'»7 


I 


currit)};  in  nature.  These  ores  are  confined  to  a  belt  oc- 
cupyiiij^  the  eastern  part  of  tlie  district,  and  nearer  to  the 
lin;^baek  region  of  the  phiins  than  any  other  important  ore 
deposits  in  Colorado. 

West  of  this  belt  in  the  Caribou  district  the  ores  are 
argentiferous  galena,  with  brittle  silver.  In  the  Ward  dis- 
trict pyrites  abound,  and  where  it  is  decomposed  the  gold 
is  free.  The  pyrites  though  gold-bearing  are  dirficult  of 
reduction. 

The  pegmatite  veins  containing  the  ore  stand  at  a  high 
angle  and  are  often  very  wide,  but  the  rich  ores,  especially 
the  tellurides,  are  concentrated  in  thin  streaks  and  not 
very  continuous  bodies.  The  gangue  or  vein  material 
is  simply  an  alteration  of  the  adjacent  granite,  or  gneis- 
sic  country  rock,  into  a  more  sparry,  larger  crystalline 
form,  consisting  of  (luartz  feldspar  and  some  mica.  This 
is  impregnated  with  rich  mineral  whose  source  is  probably 
not  far  to  find,  the  metal  elements  being  microscopically 
or  chemically  diffused  through  the  mineral  elements  com- 
posing the  adjacent  country  rock,  which  is  sometimes  por- 
phyry, and  at  others  gneiss.  This  impregnation  has  taken 
place  either  along  the  contact  of  an  eruptive  rock  with  the 
country  rock  granite,  or  else  in  a  pre-existing  vein  of  peg- 
matite, or  along  some  fault  or  jointing  plane  in  the  coun- 
try rock  itself  which  has  been  favorable  to  the  concentra- 
tion and  precipitation  of  metallic  minerals  from  their 
solutions.  The  direction  of  the  veins  is  generally  between 
northeast  and  northwest,  or  east  and  west;  their  dips  are 
steep  or  vertical. 

The  quartz  of  the  pegmatite  gangue,  when  impregnated 
with  telluride  ore,  has  a  pale,  bluish-gray  and  rather  greasy 
appearance,  streaked  here  and  there  with  a  dull  blackish, 
greasy  stain,  upon  which  sometimes  the  true  telluride  min- 
erals, such  as  sylvanite,  can  be  seen,  generally  in  long  thin 
crystals  of  a  bright  tin-like  appearance.  It  is  sometimes 
called  graphic  tellurium,  because  the  crystals  crossing  one 
another  assume  the  form  of  Hebrew  characters.  Sylvanite 
is  a  telluride  of  silver  and  gold.  There  are  many  varieties 
of  tellurides,  some  rich  in  silver  and  others  in  gold,  and 
some  with  both  combined.  When  a  piece  of  gangue  con- 
taining tellurium  is  roasted,  the  gold  comes  out  in  good 
sized  globules  on  the  surface. 


1 


^ 


128 


Two  g,  eat  tnotliLT-veins.  called  the  Maxwell  and  Hoobier 
veins,  traverse  the  telluride  district  for  several  miles,  easily 
traceable  by  their  rusty  color.  One  carries  pyrites  and  tel- 
lurides,  the  other  silver  ore  and  gray  copper.  Gold  Hill 
district,  in  the  telluride  belt,  is  traversed  by  the  Hoosier 
.uangue.  Several  veins  cross  the  Hoosier  gangue  and  arc 
richer  in  its  vicinity;  in  some,  the  ore  is  a  telluride  at  the 
surface,  but  with  depth  passes  down  into  gold-bearing  py- 
rites. 

The  Ward  district  outside  the  telluride  belt  carries  copper 
andiron  pyrites  bearing  gold.  Caribou  is  silver-bearing; 
its  ores  are  galena,  copper  pyrites  and  zinc-blende  occur- 
ring in  gneiss  near  a  dyke  of  eruptive  diabase.  The  No- 
Name  vein  crosses  and  faults  the  Caribou  vein.  Its  ores 
carry  both  silver  and  gold;  the  ores  are  silver  glance,  brit- 
tle silver,  gray  copper,  galena,  copper  pyrites,  with  native 
and  ruby  silver.  The  copper  pyrites  carries  more  gold 
than  silver. 

The  granitic  rocks  near  Boulder  are  thrown  into  a 
series  of  parallel  folds,  one  series  cut  diagonally  by  another: 
The  telluride  veins  run  along  the  slopes  of  these  folds.  The 
veins  are  in  cracks  and  fissures  coinciding  with  this  folding, 
some  of  the  main  fissures  being  filled  at  once  by  porphyry 
dykes,  the  others  more  gradually  by  vein  material.  The 
veins  occur  along,  on,  and  near  these  dykes,  along  lines  at 
the  junction  of  the  more  massive  granite  with  the  bedded 
gneiss,  along  and  between  stratification  planes  of  schist, 
and  along  the  joint  planes  of  granite.  The  veins  are  due 
to  percolating  alkaline  waters  dissolving  metalliferous 
material  and  veinstone  from  the  surrounding  rocks.  It  is 
noteworthy  that  alkaline  springs  still  exist  in  the  neighbor- 
hood, as  they  do  also  at  the  mining  district  of  Idaho 
Springs.  The  veins  occur  where  the  foldings  are  abrupt, 
and  the  direction  of  the  veins  is  parallel  to  the  strike  of 
the  stratification.  As  a  rule  the  veins  are  not  of  great  ex- 
tent. A  single  vein  can  rarely  be  traced  on  the  surface  or 
beneath  it  for  more  than  600  feet.  Before  that  distance  is 
reached,  the  vein  spurs  off  again  into  another 

Where  veins  cross  at  a  small  angle  or  where  a  spur 
branches  oflE  from  the  main  vein,  accumulation  and  enrich- 
ment of  ore  takes  place.  There  are  two  courses  of  veins, 
one  east  and  west,  the  other  northeast  by  southwest ;  the 


129 

former  system  appears  to  be  the  older,  as  the  latter  faults 
it. 

The  ore  occurs  in  chimneys  or  pockets,  with  a  good  deal 
of  barren  ground  between. 

Small  veins  run  parallel  with  each  other  for  some  dis- 
tance, the  interval  filled  with  granite  or  pegmatite.  Some- 
times a  vein  pinches  out  entirely  (contrary  to  the  general 
habit  of  true  large  fissure  veins  occupying  great  fault  fis- 
sures). The  ore  streak  is  from  i  to  20  inches  wide  contain- 
ing more  of  this  blue,  greasy,  fine-grained  "  horn  quartz" 
than  the  country  rock.  Some  of  the  veins  interlace  like 
arteries  in  a  human  body.  Minute  particles  of  pyrites 
(marcasite)  often  produce  the  dark  stains  we  have  noted 
on  the  telluride  quartz.  By  moistening  the  stone,  the  tel- 
luride  minerals  and  pyrite  appear  distinctly. 

A   TYPICAL   BOULDER   COUNTY    MINE. 

A  good  typical  and  very  instructive  example  of  a  contact 
fissure,  gold-bearing  vein  is  that  of  the  Golden  Age  at  Jim- 
town,  north  of  Boulder. 

"  At  Jimtown  a  quartz-diorite  dyke  occurs,  of  light  color 
containing  much  hornblende  and  titanic  iron,  running  nearly 
through  the  street  of  the  village.  The  cliffs  at  Jimtown, 
over  500  feet  high,  are  of  quartz  porphyry,  of  white  color, 
consisting  mainly  of  large  crystals  of  quartz  and  feldspar, 
set  in  a  fine  grained  crystalline  ground  mass  or  paste." 


GOLDEN    AGE   AND   SENTINEL    VEINS. 

From  the  town,  the  road  winds  up  a  steep  mountain 
composed  of  coarse  gray  granite,  with  occasional  belts  of 
gneiss.  Here  are  located  the  Golden  Age  and  Sentinel 
mines. 

The  Golden  Age  covers  the  outcrop  of  a  quartz-porphyry 
dyke  cutting  through  the  granite.  This  dyke  varies  in 
width,  from  a  few  feet  to  about  fifty.  The  outcrop  of  the 
m  «n  ore  chute  of  the  Golden  Age  extends  along  the  "  con- 
tact" on  the  lower  side  of  the  porphyry  dyke.  At  a  depth 
of  100  feet  the  main  shaft  discloses  a  split  in  the  vein.  The 
hanging  wall  of  the  vein  continues  into  the  dyke,  but  with 
porphyry  hanging  and  footwalls,  until  a  depth  of  330  feet, 
where  it  enters  the  upper  contact  between  the  porphyry  and 


'30 


1 1 


i! 


h! 


I 


granite.  The  dyke  has  been  much  acted  upon  and  decom- 
posed by  vein-forming  agencies  in  the  upper  workings,  but 
in  the  lower  it  is  less  decomposed  and  shows  considerable 
pyrites.  The  Golden  Age  veins  are  well  defined,  present- 
ing a  banded  or  ribbon  structure.  They  are  inclosed  in  dis- 
tinct walls  with  gouge  or  selvages,  which  at  times  show 
slickensides.  The  seams  and  feeders  that  have  enriched 
both  veins  come  in  from  the  porphyry  dyke. 

The  ore  from  the  Golden  Age  contains  rich  and  magnifi- 
cent specimens  of  free  gold.  It  is  a  free  milling  ore.  When 
rich,  the  gangue  is  a  hard,  flinty,  vitreous  white  quartz. 
The  gold  is  seldom  accompanied  by  pyrites.  It  is  gener- 
ally imbedded  in  the  white  quartz  as  bright,  yellow  gold, 
in  size,  from  coarse  grains  to  nuggets  several  ounces  in 
weight;  after  it  reaches  the  lower  contact  between  the  por- 
phyry and  granite  and  enters  the  granite,  there  is  an  in- 
crease in  the  baser  metals,  such  as  zinc-blende,  galena  and 
pyrites,  but  the  ore  still  retains  its  value  in  free  gold. 

Returning  to  the  surface,  the  Sentinel  location  covers 
the  apex  of  a  vein,  which  there  appears  enclosed  in  a  belt 
of  schistose  or  gneissic  rock. 

This  vein  dips  south  at  an  angle  of  70°  and  passes  through 
the  Golden  Age  vein  on  its  course. 

The  Sentinel  vein  ore  is  entirely  distinct  from  that  of  the 
Golden  Age.  It  is  the  characteristic  bluish  horn  quartz  of 
the  tellurium  veins  of  Boulder  County,  with  characteristic 
chalcedony  quartz  crystals  and  finely  disseminated  pyrites. 
The  value  is  in  metallic  gold  and  such  tellurium  ores  as 
petzite  and  sylvanite.  Whilst  most  of  the  gold  was  de- 
posited as  native  gold,  a  portion  has  evidently  been  rendered 
free  by  partial  decomposition  of  the  tellurides.  This  ore 
is  very  rich.  The  richest  ore  usually  occurs  in  two  narrow 
seams  or  streaks  from  a  foot  to  ten  feet  apart,  the  interven- 
ing space  being  more  or  less  mineralized  country  rock.  It  is 
richest  when  in  the  schistose  rock,  and  poorest  when  it 
passes  through  the  porphyry  dyke.  The  crossing  of  the 
Sentinel  vein  through  that  of  the  Golden  Age  is  very  clearly 
marked ;  it  very  slightly  faults  the  Golden  Age  vein. 

The  gold  mines  of  Boulder  Count"  belong  to  two  dis- 
tinct periods  of  vein  formation;  to  one  belong  the  non- 
telluride  ores,  and  to  the  other  those  producing  tellurium. 
The  tellurium  veins  appear  to  be  the  later  of  the  two. 


131 


1 


The  ores  of  the  Sentinel  tellurium  vein  are  lower  grade 
where  the  vein  passes  through  the  porphyry  dyke.  This  is 
due  to  the  Golden  Age  vein  being  formed  first,  and  drain- 
ing the  dyke  of  its  disseminated  mineral  values.  The  Sen- 
tinel received  its  mineral  from  the  schistose  or  gneissic 
rocks,  and  is  consequently  richer  where  enclosed  in  those 
rocks  than  when  in  the  dyke. 

Prospectors  look  for  richer  or  larger  bodies  of  ore  when 
veins  unite  or  cross  each  other.  In  the  Golden  Age  the 
two  veins  unite  about  loo  feet  below  the  surface.  There 
are  similar  veins  of  the  same  age,  and  large  and  rich  ore 
bodies  are  found  at  their  junction.  On  the  other  hand,  the 
Sentinel  vein   of    later  age,  passing  through  the  earlier 

S     »» 1^ 


'fin 


Plate  LXIX. 

Section  of  Golden  Age  Vein,  Jimtown,  Boulder  Co.,  Colo. 

Golden  Age  vein,  produced  no  enrichment  of  the  ore 
Dodies.  Tc  form  such  ore  bodies,  the  veins  should  be  of 
contemporaneous  origin. 

The  ore  deposits  of  Gilpin  and  Clear  Creek  counties  are 
very  similar  to  those  of  Boulder,  only  they  do  not  produce 
tellurium  ores.  The  country  rock  is  the  same  granite- 
gneiss,  penetrated  here  and  there  by  porphyry  dykes.  The 
pegmatitic  veins  are  either  in  the  gneiss  or  between  the 
dykes  and  the  granite.  In  some  cases  the  porphyry 
dyke  constitutes  a  vein  in  itself,  such  as  the  Minnie,  which 


132 

is  a  felsite  porphyry,  and  the  Cyclops,  a  quartz  porphyry. 
In  Gilpin  County,  around  Central  City,  the  ores  are  a  mix- 
ture of  copper  pyrite  and  iron  pyrite  with  a  very  little 
galena  and  zinc-blende.     All  are  gold-bearing. 

The  richer  ore  occurs  in  streaks  not  over  a  foot  wide,  in 
a  compact,  fine-grained  mass  of  pyrite.  Copper  pyrite  is 
richer  than  iron  pyrite.  The  rest  of  the  vein,  often  many 
feet  wide,  carries  pyrite  irregularly  disseminated  through 
decomposed  country  rock.  The  bulk  of  these  ores  are  diffi- 
cult to  treat,  and  are  milled,  the  loss  being  40  per  cent, 
higher  in  the  unoxidized  ores  than  in  the  oxidized.  The 
veins  follow  the  cleavage  planes  of  the  gneiss,  cutting 
the  stratification  planes  at  right  angles  with  a  vertical  dip. 
The  porphyry  dykes  are  older  than  the  veins,  as  the  cleav- 
age planes  intersect  both  the  porphyry  and  gneiss  alike. 
For  an  interval  of  20  miles  between  these  mining  districts 
and  the  plains,  there  are  no  ore  deposits  of  any  importance 
known. 

In  Clear  Creek  County  the  ores  are  mainly  silver-bearing ; 
the  silver  is  derived  mainly  from  galena  and  gray  copper. 
Dykes  of  obsidian  occur  in  one  of  tho  mines  parallel  with 
the  vein,  which  is  itself  a  porphyry  dyke.  The  richest 
mineral  is  close  to  the  obsidian  dyke. 


\\ 


i  i 


FISSURE   VEINS    IN   TRUE   IGNEOUS   ROCKS. 

Whilst  most  of  our  fissure  veins  and  ore  deposits  gener- 
ally are  more  or  less  associated  with  the  presence  of  igneous 
rocks,  there  are  some  which  are  essentially  in  igneous  erup- 
tive rocks  alone. 

The  most  remarkable  of  these  are  the  fissure  veins  of  the 
San  Juan  region  in  southwestern  Colorado. 

This  region  consists  of  an  enormous  plateau  of  lavas  of 
great  thickness  resting  upon  and  originally  overflowing  a 
low  mountain  range  or  plateau  of  granitic  and  upturned 
sedimentary  rocks,  the  latter  representing  most  of  the 
geologic  periods  from  Cambrian  to  Tertiary.  The  thick- 
ness of  these  great  lava  flows,  which  were  erupted  about 
the  Eocene  period  of  the  Tertiary,  is  upwards  of  1,500 feet; 
this  lava  mass  has  been  cut  up  by  glacial  and  river  action 
by  profound  canyons,  into  a  rugged  mountain  range,  the 
summits  of  some  of  the  castellated  moimtains  reaching  a 


'J.J 


height  of  14,000  feet  above  the  sea. 
The  lava  sheets  are  also  traversed 
to  a  depth  of  1,500  feet,  more  or 
less,  by  an  extraordinary  number 
of  great  quartz-fissure  veins. 
These  veins  appear  to  fill  shrink- 
age cracks  resulting  from  the  con- 
traction on  cooling  of  the  lava 
sheets;  strictly  speaking  they  are 
rather  "gash  veins"  on  a  larger 
scale  than  "  true  fissure  veins,"  for 
they  are  mostly  limited  to  the  thick- 
ness of  the  lava  avcrflinvs  and  cease 
when  they  reach  the  underlying 
granite. 

There  appear  to  have  been  two 
principal  eruptions ;  the  first,  dur- 
ing the  early  part  of  the  Tertiary, 
covered  the  higher  region  of  the 
San  Juan  mountains  to  a  depth 
of  1,500  feet  with  an  overflow  of 
brecciated  andesitic  lava,  which 
on  cooling  developed  fissures  of 
contraction  traversing  the  lava 
mass  in  all  directions ;  these  were 
subsequently  and  slowly  filled 
with  a  hard  bluish  quartz  contain- 
ing more  or  less  ore. 

Following  the  first  grand  over- 
flow were  others  of  less  magni- 
tude, consisting  of  non-brecciated 
andesitesandrhyolites.  This  sec- 
ond dynamic  movement  produced 
locally,  fissures  extending  below 
the  horizon  of  breccia  into  the 
stratified  rocks.  These,  however, 
are  seldom  productive  below  the 
eruptive  zone.  There  are  also 
metal  deposits  in  connection  with 
still  older  eruptions  of  andesite 
and  diorite,  such  as  Mineral 
Farm,  Calliope,  etc. 


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134 


RED   MOUNTAIN, 


In  the  Red  Mountain  district  the  ore  deposits  form   a 
peculiar  group.     They  occupy  a  seres  of  more  or  less  con- 


nected irregular  chambers,  trending  downward,  probably 
channels  of  ancient  hot  mineral  springs.     The  mineralizing 


'35 

water  completely  silicified  the  surrounding  eruptive  rock 
for  some  distance  away  from  the  ore  chambers.  So  the 
ore  bodies  are  distributed  through  a  huge  irregular  column 
of  quartz  extending  to  an  undetermined  depth. 

Large  masses  of  brilliantly  colored  material  are  con- 
spicous  in  this  region.  They  have  been  acted  upon  by 
mineral  waters  circulating  through  their  crannies  and  fis- 
sures. Ore  bodies  are  occasionally  found  in  these,  and 
such  mines  are  locally  known  as  cave  mines. 

The  ores  of  the  San  Juan  are  mostly  argentiferous  gray 
copper,  copper  pyrites  and  galena  associated  with  zinc- 
blende  and  iron  pyrites  in  usually  hard  horn-quartz  matrix. 
Some  of  the  ore  locally  contains  a  high  percentage  of  bis- 
muth: others  produce  pyrargyrite  and  polybasite,  rich 
silver  minerals;  others  carry  considerable  gold,  such  as 
the  recently  discovered  gold  belt  at  Ouray.  This  belt  oc- 
curs in  Dakotah  Cretaceous  sandstone,  which  has  been 
altered  into  a  quartzite  by  the  intrusion  of  dykes  and  sheets 
of  eruptive  diorite.  One  of  these  sheets  spreads  out  in  the 
quartzite.  The  ore  occurs  at  the  top  of  the  quartzite,  at  its 
junction  with  a  bed  of  shale.  The  gold,  which  is  free  and 
enclosed  in  brown  oxide  of  iron,  doubtless  originated  from 
the  porphyry,  and  entered  the  joints  and  bedding  planes  of 
the  quartzite,  where  they  wcre  opened  by  faulting.  Above 
the  shale  the  ore  does  not  penetrate,  the  shale  acting  as  an 
impervious  resistance  to  uprising  solutions.  Ore  bodies 
also  occur  in  the  Jurassic  limestones  below  the  quartzite, 
especially  where  they  are  penetrated  by  eruptive  rocks. 

In  the  eastern  portion  of  the  San  Juan  region  some  im- 
portant gold  deposits  occur  near  Del  Norte  in  the  Little 
Annie  or  Bowen  Mine,  which  appear  to  be  a  decomposed 
dyke  of  eruptive  rock,  containing  free  gold  in  brown  iron, 
in  the  upper  portion,  and  with  depth  iron  pyrites  also  gold- 
bearing. 

CREEDE. 

At  the  newly  discovered  camp  of  Creede,  not  very  far 
from  Del  Norte,  the  fissure  veins  are  very  similar  in  char- 
acter to  those  elsewhere  in  San  Juan ;  they  are  quartz  fis- 
sure veins  traversing  andesitic  breccia  and  other  volcanic 
rocks.  The  gangue  matter  in  these  veins  is  exceedingly 
rich  in  silver-bearing  ore,  so  much  so  that  the  amethystine 


-V: 


1 36 

quartz  composing  the  gangue  or  veinstone  is  quite  in  a 
minority  to  the  ore,  and  the  vein  may  be  said  to  be  nearly 
a  mass  of  ore  from  wall  to  wall.  The  thick  lavas  of  Creede 
rest  doubtless  with  depth  upon  Carboniferous  limestone  or 
else  on  bare  granite ;  the  former  is  found  outcropping  at 
some  distance  from  Creede,  from  beneath  the  lava  over- 
flow, and  being  penetrated  by  intrusive  eruptive  rocks 
shows  signs  here  and  there  of  productive  ore  deposits  simi- 
lar probably  to  those  at  Leadville.  Creede  is  an  encour- 
aging example  to  a  prospector,  that  all  productive  veins  in 
Colorado  have  not  been  discovered  yet,  even  in  districts 
that  have  been  pretty  well  tramped  over.  Creede  had 
doubtless  often  been  more  or  less  walked  over  by  prospec- 
tors for  years  before  the  great  discovery  was  made,  and  in 
a  year's  time  we  may  hear  of  several  more  similar  discov- 
eries in  the  great  San  Juan. 


ROSITA   AND    SILVER   CLIKK. 

The  next  important  and  peculiar  igneous  district  carry- 
ing fissure  veins  is  that  of  Rosita  and  Silver  Cliff  in  the 
Wet  Mountain  Valley  near  the  edge  of  the  prairie  country 
in  southeastern  Colorado.  Here  a  local  eruption  of  con- 
siderable power  and  magnitude  and  of  comparatively  recent 
date  has  occurred.  These  eruptions,  consisting  of  andesi- 
tic,  rhyolitic  and  trachytic  material  have  built  up  cones 
and  rounded  hills  largely  of  fragmental  material  such  as 
consolidated  tuffs,  ashes,  and  breccia,  all  of  which,  as  at 
Cripple  Creek,  rest  on  granitic  basement  rock.  From  the 
fragmentary  character  of  the  rocks  it  is  evident  that  most 
of  the  eruptions  were  explosive,  alternating,  however,  with 
quieter  flows ;  in  some  cases  the  dykes  can  be  seen,  where 
some  of  the  lava  came,  at  others  the  "  necks  "or  throats  of 
the  volcanoes  themselves  filled  up  with  volcanic  boulders; 
of  such  is  the  celebrated  Bassick  Mine.  The  mine  is  in  the 
throat  of  an  old  crater  cf  andesite,  filled  with  boulders  of 
granite  and  andesite  bedded  in  gravel  and  sand.  The  ore 
of  the  Bassick  appears  as  concentric  zones  or  shells  around 
these  boulders,  as  a  replacement  of  the  gravelly  matrix. 
The  entire  mass  has  been  permeated  by  heated  waters 
which  have  decomposed  the  rocky  fragments,  depositing 
opaline  quartz  and  kaolin  in  abundance. 


'37 

The  concentric  shells  around  the  boulders  carry  alter- 
nately several  minerals,  such  as  galena,  antimony,  zinc- 
blende,  copper  and  iron  pyrites,  all  more  or  less  gold- 
bearing.  The  ore  deposition  in  this  region  seems  t'.o  have 
taken  place  at  the  close  of  the  eruptive  period,  when  the 
eruptions  were  dying  out  into  hot  springs,  fumaroles,  etc., 
and  producing  great  decomposition  of  the  lava  rocks.  The 
district  was  not  thought  much  of,  until  Mr.  Bassick  made 
his  discovery  in  the  unpromising-looking  throat  of  the  old 
volcano,  containing  a  formation  quite  anomalous,  and 
which  the  regular  prospector,  accustomed  to  true,  orthodox 
fissure  veins,  would  have  passed  by  as  very  unlikely.  So 
it  may  happen  to  future  prospectors,  that  some  very  un- 
likely formations  may  turn  out  great  riches;  hence  it  is 
well  to  keep  a  sharp  lookout  for  everything  examinable. 


A   STUDY    OF     MODERN     LIVING     VOLCANOES    TO     UNDERSTAND 
THE   CRIPPLE   CREEK    VOLCANO. 

By  far  the  most  typical,  instructive  and  important  gold 
camp  in  Colorado  and  the  West  is  that  of  Cripple  Creek. 


■'iSS^UIWiimi^' 


Plate  LXXIl. 

Stromboli  Volcano, 

To  understand  the  geology  of  the  Cripple  Creek  region  and 
gold-bearing  volcanic  regions  and  rocks  and  their  relations 
to  the  ore-deposits,  a  knowledge  of  the  phenomena  attend- 
ing modern  volcanic  eruptions  is  necessary.  Let  us  take 
that  of  the  living  volcano  of  StromI  oli,  described  by  Pro- 
fessor Judd,  as  throwing  some  light  on  the  phenomena  that 


>3« 


may  have  occurred  many  thousands  of  years  ago  in  the 
now  extinct  volcano  of  the  Cripple  Creek  district. 

From  a  point  on  the  sides  of  the  mountain  of  Stromboli. 
masses  of  vapor  issue  and  unite  to  form  a  cloud  over  the 
mountain.  This  cloud  is  made  up  of  globular  masses, 
each  of  which  is  the  product  of  a  distinct  outburst  of  the 
volcanic  forces.  At  night  a  glow  of  red  light  appears  on 
the  cloud,  increasing  gradually  in  intensity,  and  as  gradu- 
ally fading  away. 

After  an  interval  this  is  repeated  and  continues  till  the 
light  of  dawn  causes  it  to  be  no  longer  visible.  When  we 
land  on  the  island  we  find  it  built  up  of  the  "  ejecta"  from 
the  volcano  like  a  gigantic  iron  furnace  with  its  heaps  of 

cinders  and  masses  of 
slag.  The  irregular 
shape  and  surface  of 
the  land  is  due  to 
erosion  removing  the 
loose  materials  at  some 
points,  and  leaving  the 
hard  slaggy  masses 
standing  u  p  promi- 
nently as  dykes  and 
hard  portions  of  lava 
flows,  as  Pisgah,  Rhy- 
olite  Mt.  and  others 
at  Cripple  Creek  do, 
above  the  eroded  and 
more  fragmentary 
tuffs  and  breccias. 
This  great  heap  of  cin- 
ders and  slags  rises  6,000  feet  above  the  sea  bottom  with  a 
base  four  miles  in  diameter;  2,000  feet  above  sea  level  is  a 
circular  depression,  tiie  crater  of  the  active  volcano. 

Looking  down  into  the  crater  an  outburst  takes  places. 
Before  the  outburst,  many  light  curling  wreaths  of  vapor 
ascend  from  fissures  on  the  sides  and  bottom  of  the  crater. 
Possibly  this  is  the  origin  of  some  of  the  dyke-filled  fissures 
of  Cripple  Creek.  Suddenly  a  sound  is  heard  like  a  locomo- 
tive blowing  off  its  steam.  A  great  volume  of  watery  vapor 
is  thrown  up  into  the  atmosphere,  and  with  it  a  number  of 
dark  fragments  are  hurled  500  feet  above  the  crater,  some 


Plate  LXXIII. 

Map  of  Island  of  Stromboli. 


'39 

falling  on  the  '.nountain,  others  baik  itiio  the  rratcr  with  a 
loud  rattling  noif.e.     Those  rolling  down  the  mountain  are 


Plate  LXXIV. 

Stroinboli  Crater. 


Still  hot  and  semi-molten.  This  is  a  clue  to  the  origin 
of  the  fragmentary  materials  composing  the  tuflFs  and 
breccias  at  Cripple  Creek.  The  black  slaggy  bottom  of  the 
crater  is.  as  we  have  said,  traversed  by  many  fissures  emit- 
ting jets  of  vapor.     Some  of  these  are  quite  large  and  vary 

in  size  and  number 
and  position  at  differ- 
ent periods.  From 
some,  only  steam  is 
emitted  in  loud 
snorting  puffs.  In 
others  molten  mate- 
rial is  seen  welling  up 
and  flowing  outside 
the  crater.  Such  fis- 
sures when  all  erup- 
tion has  ceased  would 
be  found,  as  at  Crip- 
ple Creek,  sealed  up 
with  solid  lava  with 
a  lava  flow  on  their  tops.  From  this  liquid  mass,  steam 
escapes  in  considerable  quantities.  Within  the  walls  of 
the   fissures,  a  viscid    semi-liquid    lava   heaves    up    and 


Plate  LXXV. 

Dykes  Cutting  Beds  of  Scoria  and  Tuflf  in  the 
Wall  of  a  Crater. 


I40 

clown  and  churns  around  till  at  last  a  gigantic  bubble  or 
blister  is  formed,  which  bursts  violently  and  a  great  rush 
of  steam  takes  place  carrying  fragments  of  the  scum-like 
surface  of  the  liquid  high  into  the  air.  At  night  the  fissures 
glow  with  ruddy  light.  The  liquid  matter  is  white  hot  and 
the  scum  on  it  a  dull  red.  Every  time  a  bubble  bursts  a 
fresh  glowing  surface  is  e::posed.  It  is  the  reflection  of 
this  upon  the  clouds  of  steam  above  the  mountain  that 
causes  the  fitful  glows  of  light  we  mentioned. 

The  phenomena  show  there  arc  cracks  communicating 
with  the  earth's  interior  highly  heated  matter  beneath  the 
surface,  together  with  great  quantities  of  imprisoned  water, 
which  escaping  as  steam  gi  /e  rise  to  all  the  active  pheno- 
mena. 

What  is  popularly  supposed  to  be  flame  in  an  eruption  is 
the  reflection  on  the  cloud  of  steam  and  dust,  from  glowing 
masses  in  the  mouth  of  the  crater.  Sulphur  is  not,  as  com- 
monly supposed,  erupted  from  a  volcano,  but  is  formed  by 
the  union  of  sulphurous  acid  and  sulphureted  hydrogen 
issuing  from  volcanic  vents. 

A  volcano  is  a  steam  vent,  like  a  geyser,  which  may  be 
called  a  water  volcano, 


|i 


ORICWN    OF    FISSURES. 

Some  light  is  thrown  on  the  possible  origin  of  some  of 
the  Cripple  Creek  dykes  and  fissures  by  the  eruption  of 
Vesuvius  in  1872.  The  bottom  of  the  crater  was  entirely 
broken  up  and  the  sides  of  the  mountain  rent  by  fissures  in 
all  directions.  So  numerous  were  these  fissures  that  liquid 
matter  appeared  to  be  oozing  from  every  part  of  its  surface 
and  the  mountain  to  be  "  sweating  fire."  One  fissure  was 
enormous,  extending  from  the  summit  to  far  beyond  the 
base  of  the  cone.  This,  filled  with  a  dyke  of  lava,  is  visible 
to-day.  From  both  crater  and  fissures  enormous  volumes 
of  steam  rushed  out  with  a  prodigious  roar.  This  roaring 
was  from  explosion  of  bubbles  one  after  another,  and  the 
vapor  cloud  above  Vesuvius,  as  at  Stromboli,  was  made  up 
of  globular  masses  of  steam  ejected  at  successive  explosions. 
Each  explosion  carried  upward  quantities  of  fragments 
which  fell  back  on  the  mountain.  All  along  the  course  of 
the  stream  of  lava,  volumes  of  steam  were  thrown  off. 


i 


'  I' 


f)Rir;iV    UK    TJTFS. 

The  dischar^'e  (.f  such  laryjfo  quantities  nf  steam  eaunes 
le  atmosphere  to  be  saturated  with  watcrv  vai)..r.  which". 
condenstiiK.  falls  in  excessive  rain  storms,  nroducinir  mu 


th 


producing  mud 


PlCLYL 


Plate  LXXVI. 

Plan  and  Cross-Section  of  the  Roots  of  a  Crater.     Black  =  D..kes  Filling 

Fissures.  * 

?/tfio'^«!r"'5'^^V^^"  ^^^^"^  sweeping  along  the  loose  vol- 

?r?in1. Tri'^v^/f  "'-^  }""  '^."^^  '^"^^^  ^^y-  doubtless,  the 
Cripple  Creek  tuffs  and  breccias  were  formed. 

GASES   AND    MATERIALS     EJECTED    FROM    VOLCAXOES. 

The  most  abundant  of  the  substances  ejected  from  vol- 
canoes IS  steam,  and  with  it  many  volatile  materials,  such 


142 


as  hydrochloric   acid   ind  carbonic   acid,    also  hydrogen 
nitrogen  and  ammonia,  and  at  Cripple  Creek  fluorine  gas! 


Microacopic  Structure  of  Glassy  Lava  Showing  Microlites  and  Crystallites. 
,0, 


Microscopic  Structure  of  Some  Crystals  Showing  Microlites  and  Crystallites 

Plate  LXXVII. 

These  different  gases  at  Cripple  Creek  had  much  to  do 
with  the  formation  of  ore  deposits.     Volatile  metals,  such 


143 

as  arsenic,  antimony  and  cinnabar  are  erupted ;  these  sub- 
stances, issuing  from  volcanic  vents  at  high  temperature, 
react  upon  one  another  forming  new  compounds,  such  as 
sulphur.  Hydrochloric  acid  unites  with  the  iron  in  the 
rocks  to  form  yellow  ferric  chloride,  common  at  Cripple 
Creek,  and  looking  like  a  greenish  yellow  sulphur.  Acid 
gases  change  lime,  alkaline  and  iron  elements  into  sulphates, 
chlorides,  carbonates  and  borates,  which,  when  removed  by 
rain,  leave  a  white  substance  like  chalk,  composed  of  pure 
silica.  Beds  of  such  material  occur  not  far  from  Cripple 
Creek  and  powdered  silica  in  some  of  the  mines. 

The  lips  of  fissures  from  which  steam  and  gases  issue  are 
coated  with  yellow  and  red  incrustations  of  sulphide  and 
oxide  of  iron,  such  as  are  common  in  many  prospect  holes 
at  Cripple  Creek. 

Solid  materials  are  ejected  in  vast  quantities ;  fragments 
of  the  rock  masses  through  which  the  fissure  is  rent  are 
carried  upwards  by  the  steam  blast,  together  with  other 
matter  far  beneath  the  surface  in  a  semi-fluid  condition. 
Hence  it  is  that  at  Cripple  Creek  we  occasionally  find  frag- 
ments of  red  granite  imbedded  in  the  volcanic  breccia  torn 
from  the  throat  of  the  volcano  in  its  passage  through  the 
underlying  granite  of  the  region. 


MINERAL    AND   CHEMICAL    ELEMENTS   OF    LAVAS. 

Eight  chemical  elements  make  up  the  mass  of  lavas, 
oxygen,  silicon,  aluminum,  magnesium,  calcium,  iron, 
sodium  and  potassium.  Oxygen  makes  up  the  larger  pro- 
portion, so  that  lavas  are  mostly  oxides.  Next  is  silicon 
and  aluminum,  giving  the  quartz  and  feldspar  and  silicate 
element. 

Lavas  are  of  two  kinds,  acidic  and  basic.  Acid  lavas 
contain  eighty  per  cent,  silica,  basic  forty-five  per  cent. 
The  former  are  rich  in  potash  and  soda,  the  latter  in  lime 
and  iron;  the  former  are  commonly  light  in  color  and 
weight,  the  latter  dark  and  heavy.  Rhyolite  is  an  example 
of  an  acidic  lava,  basalt  of  a  basic  one.  The  andesites  and 
phonolites  of  Cripple  Creek  are  intermediate.  The  minerals 
composing  these  lavas  are  principally  quartz  and  feldspar, 
together  w^ith  the  dark  minerals,  mica,  augite,  hornblende, 
olivine  and  magnetite. 


144 


CRYSTALS   AND    MICROSCOPY   OF   I,AVA. 

Many  lavas  are  of  a  glassy  nature,  others  contain  many 
crystals,  some  of  large  size. 

Microscopic  sections  of  lavas  show  them  to  be  made  up 
of  a  ground  mass  of  a  glassy  character,  with  distinct 
crystals  set  in  it  like  plums  in  a  pudding. 

In  others,  the  crystals  are  so  thick  that  the  glassy  base 
can  scarcely  be  seen. 

Through  the  midst  of  the  glass,  cloudy  matter  is  observed ; 
a  higher  power  shows  this  "  nebula"  to  be  composed  of  min- 
ute particles  called  crystallites,  the  embryonic  forms  of 
crystals.     Sometimes  we  can  see  an  attempt  of  these  par- 


Plate  LXXVIIl. 

Minute  Cavities  Containitig  Liquids  in  the  Crystals  of  Kouk. 

tides  to  aggregate  into  a  geometrical  form,  sketching  out 
the  outline  of  the  large  crystal  they  intended  to  foim,  but 
weie  prevented  from  finishing,  by  the  cooling  of  the  glassy 
magma.  These  crystallites  assume  forms  like  ferns,  hairs, 
spiders,  etc. 

In  subterranean  regions  the  conditions  were  particularly 
favorable  for  the  development  of  crystals.  The  lavas 
cooled  with  extreme  slowness,  under  enormous  pressure, 
allowmg  plenty  of  time  for  the  crystals  to  form. 

Those  lavas  containing  most  soda  and  potash  (acid  lavas) 
assume  a  glassy  condition,  and  these  have  often  cooled 
near  the  surface   rapidly,  the   more   crystalline  varieties 


MS 

slowly  at  great  depth.  Obsidian  and  rhyolites  are  glassy 
types,  granite  and  some  porphyries  with  large  crystals 
are  of  the  latter  class,  whilst  andesite  and  phorolite  may 
be  intermediate.  The  latter,  however,  at  Cripple  Creek, 
may  have  cooled  quickly  near  the  surface,  and  the  crystals 
are  for  the  most  part  small. 

Besides  the  natural  imprisoned  water,  crystals  in  lavas 
are  found  microscopically  to  contain  globules,  sometimes 
filled  .vith  gas,  salt,  and  water,  which  may  add  to  the  ma- 
terials for  the  production  of  steam. 

KRUI'TIONS   OK    DUST. 

steam  escapes  from  lava  so  violently  that  the  froth  or 
scum,  called  scoria,  is  broken  up  and  scattered  in  all  direc- 
tions. This  scoria  like  pumice  is  full  of  little  holes  like  a 
sponge,  due  to  escape  of  the  steam  in  it.  Such  spongy 
scoria  is  found  scattered  over  the  hills  of  Cripple  Creek. 
During  violent  eruptions  a  continuous  upward  discharge 
of  these  fragments  is  maintained;  the  cindery  masses  hurt- 
ling one  another  in  the  air,  fall  back  into  the  vent,  or  are 
scattered  over  the  mountain.  Being  often  shot  up  again 
and  again  from  the  vent,  they  are  reduced  to  the  finest  im- 
palpable dust.  They  fill  the  atmosphere  to  such  an  extent 
as  to  bring  on  an  "  Egyptian  darkness."  This  dust,  mingling 
with  descending  rain,  forms  destructive  mud  flows,  and  sets 
or  consolidates  into  the  tufas  or  tuffs  so  abundant  at  Cripple 
Creek.  When  larger  angular  fragments  are  caught  up  and 
consolidated  with  these,  the  rock  so  formed  is  a  breccia,  as 
already  illustrated. 

Volcanic  craters,  after  having  been  formed,  are  liable  to 
be  disturbed  by  later  eruptions.  Thus  the  crater  of  Vesu- 
vius was  reduced  400  feet  by  a  later  eruption,  the  old  crater 
blown  up  and  a  much  vaster  crater  opened. 

Cripple  Creek  also  witnessed  its  second  disturbance,  after 
the  andesitic  eruption  had  ceased,  by  one  of  phonolite  lava. 


FLUIDITY   AND   OTHER    PROPERTIES   OF    1,AVAS. 

Some  lavas,  such  as  basalt,  are  reduced  to  such  a  state  of 
fluidity  that  their  streams  run  like  water  to  great  distances. 
Others  are  of  a  more  viscid,  mortar-like  consistence,  espe- 
10 


IB 


146 


cially  the  acid  lavas,  such  as  those  of  Cripple  Creek. 
These  are  apt  to  flow  but  a  short  distance  from  their 
source,  and  to  build  up  big  domes  and  thick  masses;  of 
such  a  nature  seems  the  structure  of  Nipple  Mountain, 
south  of  Cripple  Creek. 

The  peculiar  columnar  structure  often  observed  in  basal- 
tic lava  sheets,  and  in  a  rough  way  developed  in  the  phono- 
lite  of  the  cliff  above  Victor  mine,  is  due  to  cooling  and 
contraction  somewhat  in  the  same  way  as  mud  cracks  are 
formed  in  a  drying  up  pond.  A  block  of  lava  isolated  by 
these  cracks  assumes  a  polygonal  form  like  the  basaltic 
columns  of  the  Giants'  Causeway. 

During  the  cooling  down  of  lava  and  the  escape  of  steam 
and  gases,  deposits  of  sulphur,  specular  iron  and  (at  Cripple 
Creek)  fluorspar,  are  deposited.  Specular  or  micaceous 
iron  is  not  uncommon  at  Cripple  Creek.  Rock  masses  are 
completely  disguised  by  these  incrustations. 


STRATIFICATION   OF   TUFFS. 

Tuffs  and  breccias  are  often  found  stratified.  The  frag- 
mentary materials  in  falling  through  the  air  are  sorted,  the 
finer  particles  being  carried  farther  from  the  vent  than  the 
larger  ones.  Craters  built  up  of  tuffs  and  breccias  fallen 
in  the  condition  of  a  muddy  paste,  show  very  fine  stratifica- 
tion. 

Large  cones  are  built  up  of  uniformly  spread  layers  of 
more  or  less  finely  divided  material  disposed  in  parallel 
succession.  At  Cripple  Creek  the  bedding  is  indistinct, 
and  often  difficult  to  trace,  the  dip  of  stratification  being 
still  more  compressed  by  the  cross  fracturing  of  the  rocks ; 
hence  it  is  hard  to  tell  whether  the  lines  represent  cross 
fracture  cleavage,  or  bedding  planes.  In  most  volcanoes 
the  stratified  tuffs  are  cut  and  crossed,  as  at  Cripple  Creek, 
by  numerous  dykes  running  in  various  directions,  cracks 
filled  by  lava  from  below. 

Movements,  too,  have  taken  place  subsequent  to  the  accu- 
mulation and  consolidation  of  the  whole  material  as  shown 
in  Plate  LXXIX,  whereby  the  masses  are  faulted  and  fresh 
fissures  opened  in  them.  Faults  are  found  in  some  of  the 
mines  at  Cripple  Creek,  faulting  not  only  the  lavas,  but 
the  veins  also.     Cliff  sections  of  volcanoes  show  alternate 


M7 


beds  of  solid  lava,  scoria  and  tuff,  representing  different 
eruptions  or  flows. 

There  seems  an  order  and  succession  in  the  eruption  of 
the  different  varieties  of  lava.  During  the  earlier  periods 
rhyolites,  andesites  and  phonolites  are  erupted,  and  later 
basalts.  This  appears  to  be  the  case  in  the  volcanic  region 
west  of  Cripple  Creek  around  Mt.  Maclntyre,  Thirty-Nine 
Mile  Mt.,  and  Black  Mt.  The  prevalence  of  basalt  capping 
the  other  lavas  in  that  region,  together  with  the  greater 


'MJ/iimMi 


Plate  LXXIX. 

Cliff  Section,  Composed  of  Alternate  Beds  of  Lava  and  Suuria, 
Cut  by  Lava  Dykes,  and  Faulted. 

freshness  of  the  rocks,  imply  that  its  eruptions  were  some- 
what later  than  those  of  Cripple  Creek,  where  basalt  is  not 
found,  and  where  the  rocks  are  much  decomposed. 

Volcanic  eruptions  shift  their  centers  from  time  to  time, 
making  new  cones  along  a  line  of  fissure  (for  volcanoes  are 
built  upon  lines  of  fissure).  See  Plate  LXXX.  Extinct 
craters  are  frequently  filled  by  beautiful  deep  lakes.  Cones 
rise  within  cones,  and  within  great  crater  rings.  At  each 
successive  great  eruption,  the  old  cone  is  blown  away,  and 
a  new  one  formed. 

Hot  springs  contain  large  quantities  of  silica  or  quartz  in 
solution.  The  solution  of  silica  is  effected  at  the  moment 
of  its  separation  from  combination  with  the  alkali  during 
the  decomposition  of  volcanic  rocks,  and  is  favored  by  the 
presence  of  alkaline  carbonates  in  the  water,  high  tempera- 


,        -  148 

ture,  and  the  pressure  under  which  it  exists  in  subterranean 
regions.  When  the  water  reaches  the  surface  and  is  re- 
lieved from  pressure  and  begins  to  cool,  silica  is  deposited. 
So  are  the  basins  of  geysers  formed,  and  so  the  opal  and 
hydrated  quartz  we  find  in  many  of  the  Cripple  Creek 
veins,  and  in  resilicated  rocks. 

Hot  and  cold  springs  rising  in  volcanic  regions  are  charged 
with  carbonic  acid,  and  passing  through  calcareous  rocks 
dissolve  large  quantities  of  carbonate  of  lime,  and  rede- 
posit  it  in  a  crystalline  form  known  as  "  travertine."  Near 
the  base  of  Mt.  Maclntyre,  west  of  Cripple  Creek,  a  pros- 
pect is  opened  on  a  fissure  filled  with  this  substance. 

Nearly  all  eruptions  take  place  along  lines  of  fissures  (See 
Plate  LXXX).  Probably  all  volcanoes  are  located  upon 
fissures  of  some  kind,  and  even  the  general  distribution  of 


Plate  LXXX. 

Showing  Craters  Found  Along  a  Line  of  Fissure  in  the  Eruption  of  Ktna. 


volcanoes  over  the  earth's  surface  has  been  attributed  to 
lines  of  fissures,  as  if  the  earth  had  been  cracked  like  a 
glass  globe.  We  have  plenty  of  opportunities  of  seeing 
ancient  fissures  filled  with  lava  in  the  numerous  dykes  at 
Cripple  Creek,  and  in  the  greater  volcanic  region  west  of 
it;  but  so  far  no  distinct  volcanic  craters  have  been  found. 
Nevertheless  it  is  probable  that  craters  existed  along  these 
fissures,  long  since  removed  by  erosion,  or  buried  deep 
under  flows  and  surface  matter.  We  not  unfrequently  find 
at  Cripple  Creek  that  fissures  did  not  all  succeed  in  break- 
ing through  to  the  surface,  for  at  some  depths  in  the  mines 
the  apices  of  buried  dykes  are  found  and  fissures  filled  by 
vein  matter,  whose  outcrops  do  not  appear  at  the  surface. 
A  single  vein  is  followed  from  the  surface,  and  with  depth 


'49 

two  or  more  veins  are  often  encountered,  together  with 
various  small  fissures. 

Earthquakes  doubtless  accompanied  the  eruptions,  and 
developed  many  smaller  fissures,  and  further  shattered  the 
rocks.  Added  to  this  at  Cripple  Creek,  there  was  the  sec- 
ond eruption  of  phonolite,  after  the  andesite  had  ceased. 
This  second  eruption  doubtless  added  new  fissures  in  the 
efforts  of  imprisoned  vapors  to  rcrce  for  themselves  chan- 
nels to  the  surface. 


r.ASF''    AND    SOLFATARIC    ACTION. 

The  several  stages  in  the  decline  of  each  volcanic  out- 
burst are  marked  by  the  appearance  at  the  vent  of  certain 
acid  gases.  As  the  temperature  at  the  vent  declines,  the 
nature  of  the  volatile  substances  emitted  undergoes  a  regu- 
lar series  of  changes. 

In  fumaroles,  sulphurous  acid  and  hydrochloric  acid 
abound,  with  sulphureted  hydrogen  and  carbonic  acid  in 
much  smaller  proportions.  Around  these  fumaroles,  de- 
posits of  sulphide  of  arsenic,  chloride  of  iron  and  of  am- 
monia, boracic  acid,  and  sulphur  take  place.  Arsenical 
pyrites  are  a  common  associate  for  the  ores  near  the  sur- 
face at  Cripple  Creek,  and  many  rocks  are  permeated  with 
iron  pyrites. 

Where  a  volcanic  vent  sinks  into  extinction,  hydrochloric 
and  sulphurous  acids  are  first  evolved,  and  later  sulphureted 
hydrogen  and  carbonic  acid  springs.  Such  springs  are 
common  in  the  volcanic  districts  of  Colorado  to-day,  but 
we  have  long  passed  the  stage  of  the  stronger  acids,  which 
could  only  be  expected  in  the  pit  of  an  active  modern  vol- 
cano like  Kilauea.  We  may,  however,  expect  to  find  traces 
left  of  these  gases,  in  the  rocks  of  Cripple  Creek,  such  as 
a  bleaching  and  decoloration  of  the  rocks,  leaching  and 
precipitation  of  iron,  forming  those  varied  patterns  of  oxi- 
dation so  common  at  every  prospect  hole ;  also  deposits  of 
various  sulphates  and  chlorides,  rocks  deprived  of  iron  and 
alkalies  reduced  to  powdery  siliceous  masses. 

One  action  of  subterranean  springs  is  the  transportation 
of  material  in  a  state  of  solution  and  redepositing  of  it  else- 
where, especially  in  lines  of  relief  of  pressure,   such  as 


558 


!B 


150 


fissures,  shattered  rocks,  ami  decomposed  rocks  and  zones 
in  the  rocks. 

At  Steamboat  Springs,  Nevada,  metallic  gold,  cinnabar 
and  other  minerals  have  been  found  coating  the  sides  of 
fissures  from  which  living  hot  springs  issue  at  the  surface. 
In  great  volcanic  foci  the  transfer  of  various  sulphides, 
oxides  and  salts,  which  fill  veins,  has  been  effected  either 
by  solution  or  sublimation,  or  the  action  of  powerful  cur- 
rents. This  applies  to  the  veins  and  ore  deposits  in  ques- 
tion. 

As  the  igneous  activity  of  a  district  declines,  the  temper- 
ature of  the  issuing  gases  and  waters  diminishes,  till  at 
last  the  volcanic  forces  appear  to  have  wholly  abandoned 
the  region  and  been  transferred  to  another.  This  may 
have  been  the  case  with  Cripple  Creek  and  the  volcanic 
region  west  of  it,  of  apparently  later  date.  The  history  of 
a  volcanic  disturbance  is  as  follows : 

First.  The  area  is  troubled  by  subterranean  shocks  and 
earthquakes. 

Second.  The  origination  of  fissures  is  indicated  by  the 
appearance  on  the  surface  of  hot  and  carbonic  acid  springs 
and  other  gases. 

Third.  "With  increased  subterranean  activity  the  tem- 
perature of  the  springs  and  gases  increases. 

Fourth.     A  visible  rent  is  formed  at  the  surface. 

Fifth.  From  this  fissure  gas  and  imprisoned  vapor  es- 
capes so  violently  as  to  disperse  the  lava  in  clouds  of 
scoria  or  dust,  or  to  cause  it  to  well  out  in  flows. 

Sixth.  Volcanic  action  concentrates  at  one  or  several 
points,  and  the  ejected  material  accumulates  from  volcanic 
cones. 

Sometimes  the  volcanic  activity  dies  out  entirely,  leav- 
ing cones  thrown  up  along  the  line  of  fissure.  At  others, 
some  such  center  becomes  for  a  long  time  the  habitual  vent 
for  the  volcanic  forces  of  the  district,  and  a  large  cone  is 
built  up. 

When  the  height  and  thickness  of  the  cone  have  grown 
great,  the  succeeding  eruption  rends  the  sides  of  the  cone, 
producing  fissures,  quickly  filled  by  lava,  forming  radiating 
dykes  and  surmounted  by  parasitic  cones.  The  dykes  of 
Cripple  Creek  may  in  cases  represent  such  occurrences. 

When  volcanic  energies  can  no  longer  raise  material  to 


151 

the  summit  of  the  crater,  nor  rend  the  sides,  they  find  relief 
by  making  new  fissures  and  small  cones  in  the  country  out- 
side the  main  volcan;  crater.  The  numerous  phonolitic 
dykes  in  the  granitic  region  outside  of  the  main  center  at 
Cripple  Creek  may  have  so  originated.  At  last  volcanic 
energy  diminishes,  eruptions  of  lava  cease,  fissures  are 
sealed  up  with  solid  lava,  volcanic  cones  crumble  away. 

But  still  the  existence  of  heated  mater  at  no  great  depth 
is  indicated  by  outbursts  of  gases  and  vapor,  formation  of 
geysers,  mud  volcanoes  and  hot  springs.  As  the  under- 
lying rocks  cool  down,  the  issuing  jets  of  gas  and  vapor 
lose  their  high  temperature,  diminish  in  quantity,  geysers 
and  mud  volcanoes  become  extinct,  hot  springs  disappear, 
and  all  is  quiet. 

It  was  in  the  latter  or  hot  spring  stage,  that  the  ores 
were  at  Cripple  Creek  leached  from  the  volcanic  rocks, 
probably  from  great  depths  as  well  possibly  as  from  the 
sides,  and  concentrated  and  deposited  in  the  fissures,  shat- 
tered zones,  and  decomposed  rocks.  The  last  stage  is  as 
we  find  things  to-day. 


GENF.RAf,     SUMMARY    OF     PROBABLE    VOLCANIC    EVENTS   THAT 
OCCURRED    AT   CRIPPLE   CREEK. 

At  Cripple  Creek  there  was  a  volcanic  eruption  in  Tertiary 
times  due  probably  to  some  mountain  elevation  going  on  in 
the  region  of  Pike's  Peak  or  generally  in  the  mountains. 

We  may  assume  that  preluding  the  eruption  the  area  was 
troubled  by  earthquakes.  Various  kinds  of  acid  and  hot 
springs  appeared  above  the  surface,  indicating  the  fissuring 
of  the  ground  that  followed. 

At  the  bottom  of  these  fractures,  which  may  have  been 
numerous,  molten  rock  appeared,  giving  off  imprisoned 
vapor  from  bursting  blisters  of  lava.  These  shoots  of 
steam  formed  into  a  cloud  overshadowing  the  area,  and 
carried  upwards  quantities  of  scoria  and  fragments  which 
fell  back  around  the  orifice,  forming  a  crater  cone,  or  cra- 
ters. These  fragments  being  repeatedly  shot  up,  and  fall- 
ing back  into  the  crater,  were  comminuted  into  fine  dust, 
and  fell,  together  with  larger  angular  fragments,  over  the 
surface. 

The  atmosphere  charged  with  condensing  steam  gave 


'52 

rise  to  heavy  rainfalls.  The  water  descending  the  ravines 
caup;ht  up  the  volcanic  dust  and  fragments,  forming  mud- 
flows,  the  material  rapidly  setting  into  the  rocks  we  call 
tuffs  and  breccias. 

As  the  first  eruption  at  Cripple  Creek  was  of  andesite. 
these  are  called  andesitic  tuffs  and  breccias,  and  constitute 
the  principal  mineralized  rock  of  the  mining  area. 

These  tuffs  are  sometimes  stratified  by  the  materials  being 
sorted  in  the  air  by  the  water. 

After  this  first  eruption  ceased,  there  may  have  been  a 
rest  for  a  time,  the  lavas  may  have  cooled  and  consolidated, 
and  the  region  been  covered  by  various  acid  and  hot  springs 
issuing  from  fissures  caused  by  the  late  eruption. 

Then  the  district  was  a  second  time  disturbed,  this  time 
by  an  eruption  of  phonolite,  ascending  through  numerous 
rents  and  fissures,  not  only  in  the  overlying  andesite,  but 
also  in  the  granitic  region  outside  of  the  first  volcanic 
"focus,"  probably  finding  the  old  seat  of  action  too  much 
choked  by  eruptive  matter. 

This  second  eruption  added  many  new  fissures  to  the 
already  shattered  rocks,  and  gave  many  opportunities  for 
the  deposition  of  metallic  and  vein  material  deposited 
through  the  medium  of  gaseous  and  hot  spring  and  solfa- 
taric  action  which  followed  upon  the  cessation  of  the 
phonolite  eruption. 

After  the  eruptions  at  Cripple  Creek  ceased,  the  volcanic 
forces  seem  to  have  transferred  their  field  of  action  to  the 
area  west  of  Cripple  Creek  in  the  Four-mile  district.  The 
rest  is  the  history  of  to-day. 


CRIPPLE   CREKK    AS   A    PROSPECTING    FIELD. 

A  visitor  standing  on  top  of  one  of  the  hills  like  Mt. 
Pisgah,  overlooking  Cripple  Creek,  and  glancing  at  the 
various  mines  and  multitudinous  prospect  holes  speckling 
the  hills,  is  struck  with  the  compactness  of  the  mining  dis- 
trict within  the  limited  area  of  i8  square  miles.  In  this 
small  area  all  the  principal  mines  are  located,  and  one  can 
ride  ..round  the  entire  camp  in  an  hour  or  two.  Outside  of 
this  area,  there  are  as  yet  no  mines  of  importance,  though 
prospect  holes  may  be  found  for  a  circuit  of  many  miles. 


^ 


«5.? 


ANDKSnK      \Nf»    t.RANITK    AKKAS. 

He  will  observe  that  the  principal  mines  are  located 
on  the  round  smooth  hills,  on  their  tops,  slopes,  and  on  the 
gulches,  where  the  vegetation  is  mostly  grass  and  quaking 
aspen.  These  too  are  within  a  sort  of  natural  rampart  of 
more  rugged  hills  wooded  with  pine.  In  these  outlying 
hills,  only  a  few  scattered  prospects  are  visible.  The  rea- 
son for  this  is  to  be  found  in  the  geology  of  the  region,  and 
the  differences  between  the  areas  occupied  by  andesitic 
breccia  and  granite.  The  rounded  grassy  aspen-covered 
hills  representing  the  andesitic  breccia  carry  most  of  the 
ore  bodies,  and  the  principal  mines  are  restricted  to  them. 
The  more  rugged  hills  covered  with  fir  trees,  represent  the 
granite  area,  and  in  them  for  the  most  part  are  few  mines 
of  imp6rtance,  though  many  likely  prospects  are  opened 
upon  dykes  of  phonolite,  which,  so  far  as  known,  does  not 
as  a  rule  seem  to  be  so  productive  a  rock  as  the  andesite. 

There  are  intermediate  areas,  such  as  that  of  Battle  Mt., 
characterized  by  the  presence  of  both  andesitic  breccia, 
phonolite  dykes,  and  granite,  in  which  are  some  of  the 
richest  mines  of  the  district,  such  as  the  Independence, 
Portland,  Annie  Lee,  and  others. 

It  will  appear  how  important  and  useful  a  geological  sur- 
vey is  of  such  a  region,  a  fact  not  always  recognized  by 
practical  miners.  If  the  ore  bodies  are  mainly  associated 
with  the  particular  rock  called  andesitic  breccia,  it  is  well 
for  them  to  be  able  to  recognize  that  rock,  and  ascertain 
the  limits  of  its  area. 

SIGNS   THAT    LEAD    TO    PROSPECTING. 

The  next  thing  that  strikes  the  observer  is  the  prodigious 
amount  of  prospecting  holes  and  prospecting  trenches,  the 
latter  being  particularly  common.  He  may  ask  what  was 
there  in  the  general  appearance  and  character  of  this  dis- 
trict that  led  the  "  eagle-eyed"  prospector  to  suspect  the 
existence  of  ore  bodies  in  it,  or  that  it  was  "  a  kind'er  likely 
looking  place"?  Again,  how  is  it  that  it  was  so  long  over- 
looked by  the  "  eagle-eyed,"  especially  when  so  easily  ac- 
cessible? 


'54 

On  general  principles,  in  past  yearn,  miners  in  Color/ulo, 
after  the  Leadville  and  Aspen  excitement,  were  more  on 
the  lookout  for  silver  than  gold ;  they  looked  therefore  for 
rocks  like  those  of  Leadville,  with  contacts  between  por- 
phyry and  limestone,  and  every  limestone  ledge  in  the 
country  was  ransacked.  Silver  was  rarely  found  in  vol- 
canic lava  rocks,  except  perhaps  in  the  great  San  Juan 
region,  and  miners  thought  as  little  about  prospecting  un- 
promising looking  hills  of  lava,  as  they  would  the  basaltic 
caps  of  the  table  mountains  on  the  plains.  Again,  gold 
leads  do  not  show  their  ore  on  the  surface  like  some  silver- 
lead  veins.  There  is  nothing  perhaps  but  a  little  seam  of 
rust  that  might  occur  almost  anywhere,  and  in  any  kind  of 
rock.  Hence  lava  districts  of  somewhat  recent  origin 
were  overlooked,  rather  than  looked  over.  The  discovery 
of  the  gold-bearing  properties  of  the  Cripple  Creek  lavas, 
together  with  the  increased  thirst  for  gold,  turned  the 
tables,  and  now  throughout  Colorado  every  lava  formation 
is  being  prospected  with  as  much  zeal  and  indiscriminate- 
ness  as  were  the  limestones  in  the  Leadville  days,  ^he 
prospector  now  needs  to  know  volcanic  lavas  at  s'^^ht,  to 
distinguish  varieties,  and  to  know  all  he  possibly  can  about 
their  origin,  varieties  and  mode  of  occurrence.  Hence  the 
importance  we  gave  to  the  subject  in  the  preceding  re- 
marks on  volcar  oes.  A  prospector  mm'  would  at  a  glance 
consider  the  area  about  Cripple  Creek  as  worth  looking 
over;  and  the  geologist  would  consider  it  a  very  likely 
place,  not  merely  from  the  presence  of  the  lavas,  but  mainly 
from  the  great  decomposition  of  the  rocks,  and  the  evidence 
of  the  presence  of  past  solfataric  action. 


DIFFICULTIES    IN   PROSPECTING. 

But  the  "  eagle-eyed"  one  did  not  entirely  overlook  this 
district  in  the  past,  for  some  years  ago  he  was  sufficiently 
prepossessed  with  the  appearance  of  things  to  drive  a  couple 
of  short  tunnels  in  Arequa  gulch,  and  narrowly  escaped 
becoming  a  millionaire.  What  troubled  the  prospector 
was,  that  though  he  found  the  hills  covered  with  an  extra- 
ordinary amount  of  "  float,"  he  could  not  trace  this  float  to 
any  ledge  or  rocks  "  in  place."  For  the  most  part  the  hills 
were  grassed  over,  or  covered  with  vegetation ;  and  through 


T 


•55 

tlu'  turf  were  very  few  outcroppings  of  a  likely  kind,  so  far 
as  he  could  see.  There  were  no  pronunent  quartz  veins, 
or  zones  deeply  iniprej^nated  with  irt)n.  hence  he  ^^ve  up 
the  region,  mentally  wondering;  where  on  earth  all  this  rich 
float  could  have  come  from,  perhaps  solacinjf  his  mind  by 
one  of  his  igneous,  brimstony  theories  that  it  had  been  scat- 
tered over  the  country  from  a  distant  volcano,  or  washed 
there  by  flood  or  glaciers  from  some  unknown  distant 
region.  The  former  theory  after  all  was  not  far  from  the 
truth  but  the  absence  of  all  rounding  and  smoothing  of  the 
fragments  of  float  precludes  the  latter  hypothesis.  Evi- 
dences of  former  glaciation  are  remarkably  absent  from 
the  vicinity. 


THE    RKr.lON    IMPREONATF.D    WITH    ORE. 


To  those  who  have  studied  Cripple  Creek  of  to-day,  the 
source  of  this  "  float"  is  no  mystery.  Little,  if  any  of  it, 
has  been  broken  off  from  orthodox  quartz  fissure  veins,  or 
even  extracted  from  well-defined  ore  zones.  The  fact  is, 
that  the  whole  andesitic  area  is  more  or  less  impregnated 
with  the  precious  metals,  and  the  float  on  the  surface  is 
little  more  than  the  surface  debris  of  the  general  underly- 
ing rock.  There  is  scarcely  a  stone  that  you  may  kick 
with  your  foot  over  the  entire  area,  but  ..hat  will  show 
some  trace  of  gold.  On  one  hill  an  experienced  mining 
superintendent  told  me  that,  for  an  experiment,  he  went 
around  with  a  wagon  and  picked  up  the  "  float"  almost  at 
hap-hazard,  and  it  averaged  23  dollars  in  gold.  That  such 
a  "  floaty"  region  should  receive  attention  some  day  is  not 
to  be  wondered  at,  and  we  believe  Colorado  Springs  men 
were  amongst  the  first  to  give  it  serious  attention  by  open- 
ing holes  and  prospecting  trenches  almost  at  random,  re- 
sulting in  important  discoveries.  As  a  rule  even  after  this, 
the  best  mines  were  discovered  by  mere  chance  and  guess 
work,  or  by  plodding  but  blind  prospecting,  something  like 
the  Leadville  prospector  who  in  early  days  had  all  Lead- 
ville  before  him  to  prospect,  but  did  not  know  where  to 
begin,  till  sitting  down  under  a  tree  eating  his  lunch  he  saw 
a  squirrel  scratching  in  the  ground ;  he  accepted  the  happy 
omen  and  "went  down,"  so  the  story  goes,  and  of  course 


!  f? 


if 


>56 

"  struck  it  rich ;"  so  we  understand  the  Pharmacist  and  many 
other  now  noted  mines  were  discovered  at  Cripple  Creek. 


MODE   OK    I'ROSl'ECTINt;. 

This  absence  of  surface  outcrops  or  visible  leads,  when 
thQ  "  rush  '  came,  led  to  indiscriminate  and  abundant  pros- 
pecting which  has  been  kept  up  till  the  present  time,  hence 
the  extraordinary  frecklinji:  of  the  hills  with  prospect  holes 
and  trenches. 

Sometimes  they  would  select  any  piece  of  land  they 
thought,  for  some  reason  or  other  or  without  any  reason  at 
all,  likely,  and  go  to  work  to  punch  holes  and  dig  trenches 
all  over  it  to  find  something.  In  this  way  they  frequently 
came  across  enough  signs  to  warrant  putting  down  a  pros- 
pect hole,  and  holding  the  claim,  and  then  went  on  "  to 
pastures  new." 


CHARACTER   OF    FLOAT    AND   OTHER    SURP^ACE  SIGNS. 

As  we  have  said,  the  whole  region  is  covered  with  float. 
This  float  is  usually  a  somewhat  porous  piece  of  lava,  or 
andesitic  breccia,  or  tuff,  stained  with  yellow,  brown,  or 
red  oxide  of  iron,  sometimes  in  patterns  or  concentric  rings. 
It  is  often  found  to  be  honeycomoed  when  broken  with  a 
hammer.  There  is  no  visible  ore,  but  an  assay  will  most 
likely  show  traces  of  more  or  less  gold.  Again,  a  species 
of  red  porphyritic  granite  has  been  desilicated  and  robbed 
of  many  of  its  crystal  constituents,  and  left  as  a  porous 
skeleton  of  a  rock  by  the  action  of  gases  and  springs.  The 
pores  in  this  are  often  occupied  by  oxide  of  iron,  or  even 
by  crystals  of  fluorspar.  This  is  a  likely  kind  of  float. 
Honeycombed  rusty  rock  with  quartz  crystals  is  a  likely 
float,  both  of  these  representing  the  action  of  mineral  hot 
springs.  At  rare  intervals  we  may  see  a  little  of  this  oxi- 
dized rusty  rock  in  place  protruding  from  under  the  grass, 
and  if  so,  there  is  sure  to  be  a  prospect  hole  alongside  of  it. 

Bold  outcrops  of  lava  rock  are  comparatively  scarce,  and 
when  they  do  appear,  as  in  the  cliff  above  Victor  mine,  M  t. 
Pisgah,  Bahr,  and  Rliyolite  peaks,  the  rock  is  apt  to  be  so 
hard  as  to  preclude  the  probability  of  much  ore  deposit'* 
in  it. 


»57 

^  Pieces  of  rock  or  float  stained  a  violet  purple  color  bv 
fluorine  are  considered  a  good  sign  of  an  ore  body  not  far 
ott  this  fluorspar  being  found  characteristic  of  some  of  the 
richest  veins  in  the  camp;  and  fluorine  gas  was  doubtless 


0 
sr 
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a 
o 

r* 
O 

►1 


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ft 


r 


a    rs 

«  X 

o' 

s 


n 


n 
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It 


I  i 


connected  with  the  deposits  of  ore  matter,  especially  of  the 
tellurium,  the  present  matrix  of  the  gold  in  *he  deeper  parts 
of  the  mines. 


158 


Pyrites  is  not  usually  found  on  the  surface  till  the  rock 
is  broken  open,  and  tellurium  in  little  silver  scales  and 
spots,  not  till  considerable  depth  is  attained.  But  free  gold 
may  be  found  in  surface  float,  and  from  the  grass  roots 
down,  and  in  the  early  development  of  a  mine,  in  the  oxi- 
dized upper  portions,  associated  v/ith  iron  oxide  and  black 
manganese  or  "  psilomelane." 

Mi'  ceous  or  specular  iron,  is  seen  in  some  prospect 
holts;  and  localities  marked  by  evidences  of  past  hot 
spring  action,  such  as  the  appearance  of  botryoidal  chalced- 
ony or  opal,  should  be  prospected.  A  common  and  curi- 
ous marking  in  some  of  the  bleached  volcanic  lavas  is  that 
of  an  imitation  of  trees,  ferns  and  mosses,  popularly  called 
"  photographic  rock,"  scientifically  "  dendrite"  or  tree  rock. 

This  remarkable  imitation  of  nature  is  due  to  crystalliza- 
tion of  solutions  of  manganese,  a.^'^  .nay  be  compared  to 
fern-like  appearances  on  a  frosty  window-pane  in  winter, 
which  are  certainly  not  of  organic  origin,  or  in  anyway 
connected  with  the  processes  of  photograpliv.  These 
dendritic  markings  may  or  may  not  be  considered  as  signs 
of  ore.  Similiar  markings  are  very  common  in  the  por- 
phyries of  Leadville  overlying  the  silver  deposits. 


i 


SURFACE    PROSPECTING    OF    A    MINE. 


In  some  of  the  surface  discoveries  of  mines,  when  a  con- 
siderable area,  covered  by  a  blow-out  of  iron  oxid«  as- 
sociated or  not  with  purple  fluorspar,  has  been  found  to 
run  well  in  free  gold,  the  ground  is  prospected  and  de- 
veloped to  the  depth  of  a  few  feet,  and  over  a  certain  area, 
with  plows  and  scrapers,  the  material  so  obtained  being 
sent  wholesale  to  the  stamp-mill  and  often  giving  rich 
returns.  The  object  of  this  work  is  not  merely  to  get  all 
the  values  out  of  this  rich  float,  but  in  hopes  of  uncovering 
the  vein  or  veins  of  which  it  is  the  oxidized  cap  or  blossom. 
This  was  the  way  in  which  the  Deerhorn  mine  was  opened 
up,  and  its  veins  discovered  on  Summit  Hill.  The  ground 
on  the  top  of  the  hill  is  observed  to  have  been  "  gophered'' 
in  all  directions  like  the  catacombs  to  a  depth  of  about  ao 
feet,  and  over  an  area  of  a  square  acre  or  so.  This  w;*« 
done  partly  to  gather  up  and  collect  the  rich  floa^  which 


»59 

was  found  scattered  over  the  hill  nnd  partly  to  discover  the 
leads  in  place. 

This  rich  float  was  stained  with  purple  fluo-iue.  and  up- 
wards of  25,000  dollars*  worth  of  gold  was  obtained  from 
this,  the  material  being  dug  up  by  plows  and  scrapers, 
before  the  subsequently  discovered  veins  were  found  or 
worked. 

In  the  case  of  the  Anaconda  mine  on  Gold  Hill,  the  out- 
crop of  a  dyke  of  andesite  was  discovered  on  the  hillside 
covered  with  an  oxidized  crust  carrying  gold.  The  owners 
developed  this  by  an  open  quarry,  about  a  hundred  feet  in 
length  and  40  to  50  feet  deep,  from  which  they  extracted 
the  bonanza  which  made  this  mine  at  its  outset  so  cele- 
brated, and  later  proceeded  to  uncover  the  dyke  on  the  sur- 
face, to  a  depth  of  about  20  feet  along  the  entire  length  of 
their  claims,  but  nothing  comparable  with  the  bonanzas 
of  the  first  quarry  has  been  found  since  in  extension  or 
depth. 

RICHNESS   WITH    DEPTH,    ETC. 

Many  of  the  mines  shipped  their  best  ore  from  the  grass 
roots  and  upper  oridized  portions  of  the  veins,  which  con- 
tained free  gold  and  were  free  milling.  With  depth  some 
of  these  mines  have  not.  done  nearly  as  well,  especially 
when  they  reached  the  unoxidized  zone,  ..way  from  surface 
influences,  and  the  ore  was  found  v/rapped  up  in  tellurium 
or  iron  pyrites. 

The  palmiest  days  of  many  a  gold  camp  are  its  earliest 
days. 


SUGGESTIONS   TO   PROSPECTORS. 

In  the  more  productive  area  the  prospector  will  do  well 
to  keep  to  the  andesitic  breccia,  and  follow  the  signs  we 
have  mentioned.  Outside  of  this  area  his  course  may  be  a 
little  different,  as  then  he  is  in  the  granite  district,  and  looks 
out  for  the  appearance  of  dykes  of  phonolite,  rarely  more 
than  a  few  feet,  though  sometimes  many  yards,  in  width,  and 
easily  distinguished  from  the  red  granite  by  their  light 
gray  or  white  color.  These  dvkes  do  not  often  appear  out- 
cropping in  the  granite  clifl^s,  but  are  more  commonly  to  be 
found  buried  beneath  the  debris  and  grass  of  the  slopes. 


i6o 

On  these  he  may  find  no  indication  and  trust  to  hap-hazard 
trenching;  or  a  few  stray  pieces  may  lead  him  to  the  spot. 

The  more  rusty,  oxidized  and  decomposed  the  phonolite, 
the  more  likely  it  is  to  carry  gold;  at  times  he  mav  find  ore 
and  free  gold  in  the  dyke  itself,  but  more  often  at  its  con- 
tact, on  one  or  both  sides,  with  the  granite.  There  he  is 
likely  to  find  a  crevice  filled  with  clay  or  iron-oxide,  car- 
rying seams  and  cavities  lined  with  quartz  crystals  or 
stains  of  purple  fluorspar. 

Sometimes  he  may  find  the  coarse  granite,  as  in  the  case 


Plate  LXXXII. 

A  Section  Moose  Mine  Vein,  Raven  Hill.  i.  Country  Rock  Breccia,  z.  Yel- 
low Jasper,  with  Cavities  of  Quartz  Crystals.  3,  Blue  Gray  Jasper,  with 
Seams  of  Quartz  and  Iron  containing  Gold. 

of  the  Independence  mine  on  Battle  Mt.,  just  at  the  contact 
with  the  dyke  of  lava,  to  be  very  rotten,  much  honey- 
combed and  robbed  of  many  constituent  minerals,  and 
these,  by  replacement  with  metals,  may  yield  him  the 
richest  ore.  Again,  the  dyke  between  walls  may  be  re- 
duced to  a  blue  or  yellow  jaspery  clay,  with  a  vertical  lami- 
nation or  cleavage,  the  lines  of  cleavage  filled  with  quartz 
and  iron  oxide  (See  Plate  LXXXII) ;  in  such  lines  he  is 
apt  to  find  the  richest  ore. 

After  opening  a  prospect,  the  ore  signs,  consisting  of 
stains  of  oxide  of  iron  and  manganese,  instead  of  pursuing 
an  even  or  regular  course  are  apt  to  scatter  amongst  the 
infinite  number  of  crevices  shattering  the  rocks,   no  one 


■i   1: 


i6i 


little  lead  being  of  sufficient  richness  to  follow  with  profit, 
and  the  whole  body  bet.veen  walls  scarcely  paying  to  work. 

The  ore  sig^s  often  follow  a  very  uneven  course,  now 
lying  upon  a  fairly  defined  wall,  then  running  for  a  dis- 
tance into  one  wall  or  other,  or  again  following  the  main 
course  of  the  creviced  lava  breccia  between  walls,  now  in 
pockets  and  crevices,  again  scattered,  or  again  impregnat- 
ing the  porous  and  decomposed  rock.  There  are  very  few 
true,  well-defined  veins  in  the  camp;  the  ore  rather  impreg- 
nates certain  ill-defined,  shcittered  zones  of  rocks  between 
certain  ill-defined  boundaries  called  walls.  At  others  the 
ore  occupies  narrow  cleavage  planes  in  the  rock,  of  which 
there  may  be  two  or  three  in  a  mine,  some  of  them  produc- 
tive, others  very  little  so.  Ore  bodies  in  the  harder  or 
more  compact  rocks,  such  as  the  Buena  Vista  and  Victor 
mines,  are  apt  to  have  something  more  like  defined  veins 
and  defined  walls.  In  some  cases  surface  signs  have  been 
poor,  and  with  depth  have  done  well ;  the  exact  opposite 
has  often  been  the  case.  Some  mines  have  been  good 
from  bottom  to  top,  but  we  have  to  be  careful  here,  as  in 
most  gold  camps,  of  the  old  fallacy  of  "  richness  with  depth." 
There  is  little  more  criterion  for  this  than  in  other  camps, 
and  many  a  once  famous  mine  is  looking  vainly  with  depth 
for  its  lost  bonanza,  though  in  other  respects  doing  fairly 
well. 

As  regards  the  granite  itself,  we  have  heard  of  few  ordi- 
nary quartz  fissure  veins  unaccompanied  by  lava  intrusions 
proving  productive. 

The  fine  grained,  red,  eruptive  granite  on  Barnard  Creek, 
north  of  Cripple  Creek,  has  shown  a  promising  ore  body  in 
a  lava  dyke  in  the  granite,  which,  singularly  enough,  pro- 
duces a  fine  grained  galena,  rich  in  gold.  Galena  is  quite 
a  rare  ore  in  Cripple  Greek.  Green  carbonate  of  copper 
stains  appear  at  times  in  the  schists  and  gneisses,  but  none 
so  far  productive. 

The  railroad  from  Canyon  City  to  Cripple  Creek  did 
some  good  prospecting  work  in  the  granite  area,  its  cut- 
tings exposing  quite  a  number  of  phonolite  and  other 
dykes,  together  with  some  granitic  veins. 

Outside  of  Cripple  Creek,  in  the  great  volcanic  area  to 
the  north,  between  Cripple  Creek,  and  South  Park,  is  a 
fair  prospecting  field.     The   rocks  are   mainly   granites, 
II 


l62 

rhyolites.  trachytes,  andesites  and  basalt,  the  products,  as 
at  Cripple  Creek,  of  a  series  of  volcanic  eruptions,  of  which 
the  latest  appears  to  have  been  basalt,  which  commonly 
caps  the  other  and  lighter  colored  lavas. 

The  rocks  in  this  region  are  for  the  most  part  less  decom- 
posed than  those  at  Cripple  Creek,  which  is  not  so  favor- 
able a  sign.  Here  the  prospector  should  look  out  for  all 
signs  of  decomposition,  such  as  we  observed  at  Freshwater 
district,  a  not  unlikely  spot.  The  very  hard,  massive  rocks 
are  not  likely  to  be  productive,  such  as  the  hard  black 
basalts.  The  lighter  colored  and  more  decomposable  lavas 
offer  a  better  chance. 

Centers  of  eruption,  such  as  relics  of  old  craters  and 
dykes  from  v/hich  these  different  lavas  issued,  should  be 
sought  for  and  prospected.  Balfour,  a  small  mining  camp 
at  the  north  of  this  area,  is  established  among  granite  and 
eruptive  rocks,  which  have  been  found  to  be  mineralized 
by  pyrites.  The  granites  here  have  several  fissure  veins 
and  dykes  in  them,  showing  considerable  disturbance  to 
have  taken  place  in  that  neighborhood.  The  low  hills  in 
which  the  prospect  holes  are  located  are  capped  with  basalt, 
apparently  resting  on  volcanic  tuffs  and  other  lavas.  So 
far,  nothing  very  productive  has  been  found,  though  here, 
as  elsewhere,  much  is  hoped  for  with  depth.  Singularly 
enough,  in  one  of  these  veins  in  lava,  \;e  noticed  a  tarry 
substance  or  inspissated  bitumen  in  the  cavities  of  the  rock, 
an  unusual  occurrence  in  fissure  veins  or  in  volcanic  rock. 


CHAPTER   XII. 


ORE   DEPOSITS  IN    SEDIMENTARY   ROCKS. 

BLANKET   ORE    DEPOSITS,  CONTACT   DEPOSITS. 

This  great  second  class  of  ore  deposits,  occurring  prin- 
cipally in  Paleozoic  limestones  at  contact  more  or  less  with 
intrusive  sheets  of  porphyry,  is  mainly  represented  in  Colo- 
rado by  the  Leadville  and  South  Park  mining  district,  the 
Kokonio  and  Red  Cliff  districts,  and  the  Aspen  and  Gun- 
nison districts,  though  locally  here  and  there,  wherever 


'63 

Paleozoic  strata  accompanied  by  igneous  rock  may  be  ex- 
posed, silver  mines  may  be  fotmd.  We  will  begin  with 
Leadville  and  South  Park  as  primarily  instructive  and 
typical. 

SOUTH    PARK    ORE    DEPOSITS. 

The  basin  plain  of  South  Park  is  underlaid  by  sedimen- 
tary rocks  from  the  Cambrian  below,  to  the  Upper  Creta- 
ceous on  top.  These  strata  slope  up  to  the  crest  of  the 
Mosquito  range  on  the  west,  where  they  become  violently 
folded  and  faulted  and  eroded. 

SiaeASAal*  '/■'M^y^^^^  l"     =?iK^>0 

Contact  Orm  S'/^^U^m^^m9^^^^<  ^-^     ^ 

'  I        I     I      f    r  Hljiiii       'i|W'l'    '        Cimtaet  Dtpoatt 

CA  Mtm    ^^^^^^^^^li^'^/.'^^^ "  Louxr  CarboniArou* 
J^^I^^^^^^^^^^^^  Z^rerd  etolomitie 

Plate  LXXXIII. 

Section  of  Leadville  Cliff. 

The  mineral  developments  are  on  the  slopes  of  this  range 
on  both  sides  of  it. 

The  order  of  succession  of  strata  forming  the  structure  and 
cliffs  of  the  range  and  resting  on  the  granite,  is  as  follows, 
beginning  with  the  lowest : 

Feet  thick. 

Cambrian  quartzite '°o 

Silurian  drab  limestone  (dolomite) 200 

Lower  Carboniferous  blue  limestone 200 

Middle  Carboniferous  sandstones  and  guartzite  (Weber  grits).  .2,000 
Upper  Carboniferous  limestones,  reddish  sandstones 1,000 

Total 3.6oo  to  4,000 


164 


These  formations  have  been  traversed  by  eruptive  quartz- 
porphyry  and  porphyrite  dykes  and  intrusive  sheets.  'The 
dykes  occur  principally  in  the  Archaean,  but  the  intrusive 
sheets  are  many  and  are  spread  out  between  the  quartzites 
and  limestones  of  the  Cambrain,  Silurian  and  Carboniferous. 

The  connection  hchvcen  the  eruptive  masses  and  deposition  of 
ore  is  very  marked.  The  ore  bodies  are  a  concentration  of 
the  metallic  minerals  originally  disseminated  through  the 
mass  of  these  eruptive  porphyries  and  deposited  along 
their  plane  of  contact  with  the  sedimentary  beds,  and  by 
metasomatic  substitution  extending  more  or  less  into  the 
mass  of  the  latter. 

On  mountains  Lincoln  and  B'ross,  in  the  principal  mines, 
the  ores  are  mainly  argentiferous,  yielding  galena  and  its 
products  of  decomposition,  viz.,  carbonate  of  lead  (cerussite) 
and  sulphate  of  lead  (anglesite)  with  chloride  of  silver. 
Barite  (heavy  spar)  is  a  common  gangue  or  vein  rock  espe- 
cially in  the  richest  parts  of  the  mine.  Iron  pyrites  decom- 
posed and  passing  into  a  hydrated  oxide  of  iron,  together 
with  a  black  oxide  of  managnese,  give  to  the  ore  its  rusty 
and  black  color. 

The  deposits  occur  in  irregular  bodies  or  pockets  often 
of  great  size,  in  the  blue  limestone,  near  its  upper  surface, 
but  not  always  easy  to  find  or  follow.  This  limestone  was 
originally  covered  by  a  sheet  of  quartz-porphyry  which  has 
been  locally  removed  from  the  ore  deposits,  but  exists  in 
the  peak.  This  porphyry,  generally  recognized  by  its  large 
feldspar  crystals,  is  called  Mt.  Lincoln  porphyry  and  is  quite 
common  and  characteristic  of  Western  Colorado.  In  the 
Dolly  Varden  mine  the  ore  occurs  in  the  limestone  at  con- 
tact with  a  vertical  dyke  of  white  quartz-porphyry. 

In  the  Fanny  Barrett  mine,  on  Loveland  Hill,  rich  de- 
posits of  galera  and  anglesite  occur  in  a  vertical  fissure 
(probably  a  gash  vein)  crossing  tiie  hill  from  side  to  side 
and  traversing  the  Paleozoic  strata  at  right  angles  to  their 
dip.  but  probably  not  entering  into  the  underlying  granite. 
This  mine  was  discovered  by  noticing  little  pieces  of  iron 
following  a  general  line  across  the  hill. 

In  Buckskin  Gulch  the  Phillips  mine  is  an  immense  mass 
of  gold-bearing  iron  pyrites,  deposited,  in  beds  of  Cam- 
brian quartzite  near  a  dyke  of  quartz-porphyry.  This  mine 
was  discovered  by  its  rusty  outcrop  being  exposed  along 


•65 

the  edge  of  the  stream.  At  first  this  crust  of  iron  oxide  was 
loose  enough  to  be  panned  for  gold  with  good  success  by 
the  old-timers,  and  afterward  milled.  But  when  the  hard 
pyrite  set  in,  the  ore  was  found  to  be  too  low  grade  to  pay 
for  roasting  and  smelting,  and  for  many  years  lay  idle, 
en 


The  Criterion  in  the  cliff  above  this  consists  of  large  caves  in 
Cambrian  quartzite.  still  partly  occupied  by  oxidized  gold- 
bearmg  iron  ore.  and  galena-bearing  silver  close  to  a  />or. 
phynte  dyke.  ^ 


i66 


The  London  mine  in  Mosquito  ^^ulcli  is  peculiar  and  in- 
structive as  bein^  involved  in  the  great  London  fault. 
There  are  two  strong  veins  or  deposits  of  pyrites  carrying 
both  gold  and  silver;  the  gangue  of  one  is  quartz,  the  other 
calcite.  They  occur  in  the  limestone  in  connection  with 
an  int rustic  bed  of  white  porphyry.  These  deposits  stand  in 
a  vertical  position,  the  beds  containing  them  having  been 
turned  up  abruptly  against  the  great  London  fault,  by 
whose  movement  the  Archjean  granite  rocks  forming  the 
eastern  half  of  London  Mt.  are  brought  up  into  juxtaposi- 
tion with  the  Silurian  and  Carboniferous  beds  at  its  western 
point. 


London  HiU 


i^':- 


/"^  t^.v§ 


/ 


Ar^yry 


\n 


^^^ 


Plate  LXXXV. 

The  London  Mine  Fault. 

Going  south  along  the  Mosquito  range  the  intrusive  por- 
phyries diminish  in  extent  and  with  them  also  the  mineral  deposits. 

The  Sacramento  mine  is  a  good  example  of  a  "  pocket" 
mine.  Rich  bodies  of  galena  and  rich  decomposed  ores 
have  been  found  at  uncertain  intervals  in  a  series  of  pockets 
or  cavities.  Some  of  these  pockets  or  cavities  are  empty, 
and  lined  with  modern  stalactites,  others  contain  loose 
sand,  with  pebbles  of  rich  ore,  others  are  quite  full  of  rich 
ore  deposits.     These  deposits  are  difficult  to  follow  with 


: 


107 

any  degree  of  certainty,  unci  much  of  the  prohts  made  in 
the  rich  pockets  have  been  used  upinblimlly  *  gophcrinjf  " 
after  other  pockets.  From  some  of  these  i  hambers  open 
fissures  or  joint  planes  ascend  to  the  surface.  The  lime- 
stone was  originally  rapped  by  a  porphyry  which  has  since 
been  eroded  off.     This  porphyry  doubtless  supplied  the  ore. 


LEADVII.I.K   IHSTRK   r. 

The  western  boundary  of  this  district  is  the  Sawatch 
range  of  Archiean  granite.  The  slope  of  the  Mosquito 
range  in  the  east  and  the  hills  o\\  the  north,  forming  the 
watershed  between  the  (»rand  and  Arkansas  rivers,  have 
a  basis  of  Archtean  granite  and  gneiss  more  or  less  covered 
by  patches  and  remnants  of  the  Paleozoic  formations,  />., 
Cambrian,  Silurian  and  Carboniferous,  which  have  escaped 
erosion. 

Their  lower  position  relative  to  corresponding  beds  on 
the  eastern  or  South  Park  side  of  the  Mosquito  range  is 
due  in  part  to  faulting,  and  in  part  to  folding  of  the  beds. 

Within  these  Paleozoic  formations,  these  beds  of  quartzite 
and  limestone,  //urf  /s  an  enormous  development  of  eruptive 
rocks,  principally  quartz-porphyries  partially  occurring  as 
dykes  but  generally  as  immense  intrusive  sheets  following 
the  bedding  plane  of  the  sedimentary  rocks. 

Glaciers  have  been  at  work  also  in  this  neighborhood. 
A  huge  "  mer  de  glace"  occupied  the  great  valley  of  the 
Arkansas  to  whose  bulk  numerous  side  glaciers  contributed ; 
these  glaciers  have  carved  and  sculptured  the  mountains. 
In  the  flood  period  following  the  first  glacial  epoch  a  lake 
was  formed  occupying  the  head  of  the  Arkansas  Valley. 
The  stratified  gravel  and  sand  beds  which  were  deposited 
at  the  bottom  of  this  lake  now  form  terraces  bordering  the 
valley  of  the  Arkansas  River.  These  beds,  known  as 
"  wash"  or  placer  grounds,  yield  gold  and  are  open  to 
further  development.  Leadville  is  the  center  of  the  min- 
ing district,  the  ores  are  argentiferous  galena  and  zinc- 
blende.  They  are  smelting  ores.  Their  value  is  increased 
by  their  having  been  oxidized,  the  lead  occurring  as  car- 
bonate, th?  silver  as  chloride  in  a  clayey,  or  else  silicious, 
mass  of  hydrated  oxides  of  iron  and  manganese. 

The  ore   is  principally  confined  to  the  horizon  of  the 


i68 


"  blue"  or  Lower  Carboniferous  liniestone,  covered  by  an 
intrusive  sheet  of  "  white  Leadville  quartz-porphyry."  The 
ore  bodies  occur  not  only  at  the  immediate  contact  of  these 
rocks,  but  extend  down  in  irregular  pockets  and  chambers 
int(»  the  mass  of  the  limestone,  sometimes  to  a  depth  of 
loo  icet.  Sometimes  the  ore  completely  replaces  the  lime- 
tone  between  two  sheets  of  porphyry,  as  in  the  "  Col.  Sellers 
mine,"  Chrysolite,  Little  Pittsburg,  and  <m  Fryer  Hill.  A 
few  ore  bodies  occur,  carrying  more  gold  than  silver,  found 
at  other  horizons,  usually  as  "gash"  veins  nmning  across 
the  stratification  or  along  bedding  planes.  Such  are  the 
Colorado  I*rince  in  quartzite,  the  Tiger  and  Ontario  in  the 
Weber  grits  of  the  Middle  Cnrboniferous. 

The  "  Printer  Boy,"  one  of  the  oldest  mines,  has  produced 
a  good  deal  of  gold,  found  as  free  gold  associated  with  car- 
bonate of  lead  and  galena,  passing  down,  as  is  usual  in 
gold  mines,  into  unaltered  auriferous  iron  and  copper 
pyrites,  which  occur  in  a  body  of  quartz-porphyry  along  a 
vertical  cross-joint  or  fault  plane  in  the  porphyry.  The 
gangue  is  a  white  clay  resultmg  from  decomposition  of  the 
quartz-porphyry,  and  though  the  clay  ore  is  rich,  it  shows 
no  minerals  to  the  eye. 

The  Paleozoic  formations,  together  with  the  intrusive 
porphyry  sheets  sandwiched  in  between  them,  have  been 
compressed  into  gentle  folds,  and  where  the  fold  was  at  its 
greatest  tension,  a  series  of  parallel  faults  have  occurred 
having  a  general  north  and  south  direction;  their  uplifted 
side  is  generally  to  the  east. 

The  prevailing  eruptive  rock  is  the  "  white  Leadville 
porphyi  y,"  occurring  generally  above  the  blue  limestone 
but  also  in  places  below  it  and  at  other  horizons. 

There  are  also  other  intrusive  sheets  of  different  varieties 
of  quartz-porphyry.  The  ground  is  generally  buried 
beneath  a  hundred  feet  of  glacial  moraine  material,  local- 
ly called  "  wash." 

The  general  geology  of  the  South  Park  and  Leadville 
region  has  been  so  elaborately  traced  by  the  labors  of  the 
U.  S.  Geological  Survey  that  we  cannot  do  better  than  give 
an  abstract  of  their  report  in  this  connection : 


169 


MOSQUITO    RANCE. 

A  Study  of  this  ranjcc  is  necessary  to  the  undurstanditiK 
of  the  Lcadville  ore  deposits,  which  occur  on  its  western 
side.  It  comprises  a  length  of  19  miles  alon^  the  crest  of 
the  range,  and  in  width  including  its  foothills  bordering  tlie 
Arkansas  Valley  on  the  west,  and  South  Park  an  the  east, 
a  slope,  in  one  case  ;;f  7 -^  miles,  and  in  the  other  of 
about  9  miles.  All  of  it  is  about  10,000  feet  above  the  sea 
level. 

The  range  has  a  sharp  single  crest  trending  north  and 
south..  To  the  west  this  crest  presents  abrupt  cliffs  de- 
scending precipitously  into  great  glacial  amphitheatres 
at  the  head  of  the  streams  flowing  from  the  range.  Mts. 
Hross,  Cameron  and  Lincoln  constitute  an  independent  up- 
lift. The  abrupt  slope  west  of  the  crest  is  due  to  a  great 
fault  extending  along  its  foot,  by  which  the  western  con- 
tinuation of  the  sedimentary  beds,  which  slope  up  the  east- 
cm  spurs  and  cap  the  crest,  are  found  at  a  very  much  lower 
elevation  on  the  western  spurs.  The  jagged  step-like  out- 
line of  the  western  spurs  is  duo  to  a  scries  of  minor  parallel 
faults  and  folds. 

The  secondary  uplift  of  Sheep  Mountain  on  the  eastern 
slope  is  due  to  a  second  great  fold  and  fault. 

The  elevation  of  Mount  Lincoln  is  the  result  of  the  com- 
bination of  torces  which  have  uplifted  the  Mosquito  range 
and  those  which  built  up  the  transverse  ridge  separating 
the  Middle  from  the  South  Park. 

The  range  has  been  sculptured  by  glaciers  into  canyons, 
and  the  Arkansas  valley  is  covered  with  horizontal  terraces 
representing  the  distribution  of  material  by  waters,  on 
the  melting  of  the  glaciers. 

In  the  seas  of  the  Paleozoic  and  Mesozoic  eras  which  sur- 
rounded the  Sawatch  islands,  some  10,000  to  12,000  feet  of 
sandstone,  conglomerates,  dolomitic  limestones  and  shales 
were  deposited.  Towards  the  close  of  the  Cretaceous, 
eruptions  occurred  by  which  enormous  masses  of  eruptive 
rock  were  intruded  through  the  Archican  floor  into  the 
overlying  sedimentary  beds,  crossing  some  of  the  beds,  and 
then  spreading  out  in  immense  intrusive  sheets  along  the 
planes  of  division  between  the  different  strata. 


The  'ntrusive  force  must  have  been  very  j^reat.  since 
comparatively  thin  sheets  of  molten  rock  were  forced  con- 
tinuously for  distances  of  many  miles  between  the  sedimen- 
tary beds. 

That  the  eruptions  were  intermittent  and  continued  for 
a  long  time  is  shown  by  the  great  variety  of  eruptive  rocks 
found.  That  this  eruptive  activity  preceded  the  great 
movement  at  the  close  of  the  Cretaceous,  which  uplifted 
the  Mosquito  range  as  well  as  the  other  Rocky  Mountain 
ranges,  is  proved  by  the  folding  and  faulting  of  the  por- 
phyry eruptions  themsehes. 

In  the  period  inteivening  between  the  close  of  the  Cre- 
taceous and  the  deposition  of  the  Tertiary  strata,  duriiig 
which  the  waters  of  the  ocean  gradually  receded  from  the 
Rocky  Mountain  region,  the  pent-up  forces  of  contraction 
in  the  earth's  crust,  which  had  been  long  accumulating, 
found  expression  in  dynamic  movements  of  the  rocky 
strata,  pushing  together  from  the  east  and  the  west  the 
more  recent  stratified  rocks  against  the  relatively  rigid 
masses  of  the  Archaean  land,  and  thus  folding  and  crump- 
ling the  beds  in  the  vicinity  of  the  shore  lines. 

The  crystnllne  and  already  contorted  beds  of  the  Archaean 
doubtless  veceived  fresh  crumples  in  this  movement. 

A  minor  force  also  acted  north  and  south,  producing  gentle 
lateral  folds  along  the  foothills  at  right  angles  to  the  trend 
of  the  range.  These  movements  were  not  paroxysmal  or 
sudden  and  violent,  but  protracted  for  an  enormous  lapse  of 
time,  and  appear  to  be  continued  in  diminished  force  up  to 
the  present  day. 

MINERAL    DEPOSITION, 

It  was  during  the  period  intervening  between  the  intru- 
sion of  the  eruptive  rocks  and  the  dynamic  movements 
which  uplifted  the  Mosquito  range,  that  the  original  de- 
positions of  metallic  minerals  occurred  in  the  Leadville 
region  in  the  form  of  metallic  sulphides,  though  now  they 
are  found  largely  oxidized  and  in  other  combinations. 
They  were  derived  from  the  eruptive  rocks  themselves 
and  are  therefore  of  later  formation  than  they.  Their  hav- 
ing been  folded  and  faulted  with  them  shows  that  they 
must  have  been  formed  before  the  great  Cretaceous  uplift, 
and  therefore  they  are  older  than  the  Mosquito  range  itself. 


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No.  I.   IdMl  Section,  s^Ming  Pakonoie  and  Mesonoie  Strata,  with  iMtmsiOh  •  ofBruttive 

Islands,  prior  to  the  gr tat  Mountain  Ettvat 


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No.  ».    /deal  Section,  showings  reault  of  the  great  Post -Cretaceous  I 


tStUtrntlum 


No.  s.   Average  Section  ofLeadviUe  District,  Mosquito  Range  and  South  Parh  as  i, 

Plate  LXXXVl 

Sections  to  Illuatrate  the  Gradual  Geological  Development  of  the 


ic^Shet. 


t/Unei  TW'oM 


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Mii««3S'jT«*«> 


CUoroflTo  ./>«>•«  lUtn^ifm  MltUnxdt 

/Jf^'i/'*''-^*'^^"^^'*^*'^' A^7*'*^^'*/**  ^"otoieSec, between  SMuatckand  Front  Jfangt 
t  great  Mountatn  Eievatton  at  Close  of  Cretaceous.  *  ^" 


Crmteicmo€*s 

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Ootoi-cictof^crrKt  Aen\grm  V^HfC 


t  great  Post -Cretaceous  Uplift  and  the  folding  Hp  of  the  Mosquito  Range. 


Wimfmitltlia'vr*  StuthPhtrlt  Begirt  Catorma^^mntAtf^* 

nge  and  South  Parh  as  it  is  To^ay,  showing  result  of  Faulting  and  subsequent  Erosion. 

Plate  LXXXVI. 


ical  Development  of  the  Leadville  and  South  Park  Region,  Colorado. 


"■•il»  fl.'.(Jif Wl !!P_i  HtJ.KH"! 


I  ■iimttmmrn^liifmmrmmi^mmimiim'Wiim 


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«7' 


The  deposits  were  formed  by  the  uction  of  percolating 
waters  taking  up  certain  ore  materials  in  their  passajfe 
through  neighboring  rocks,  and  depositing  them  in  more 
concentrated  form  in  their  present  position.  This  may 
have  taken  place  while  the  sedimentary  beds  were  still 
covered  by  the  waters  of  the  ocean,  and  the  waters  there- 
fore may  have  been  derived  from  it,  or  the  area  of  the  Mos- 
quito range  may  have  already  emerged  from  the  ocean 
and  the  waters  have  been  estuarine.  The  uplift  of  the 
Mosquito  range  consisted  of  a  series  of  folds  fractured  by 
faults.  The  crest  is  formed  by  the  Mosquito  fault,  another 
parallel  fracture  is  the  London  fault.  The  greatest  move- 
ment is  towards  the  center  or  Leadville  region,  dying  out 
at  either  end  north  and  south;  the  greatest  displacement 
is  10,000  feet.  Whatever  cliffs  may  have  originally  been 
formed  by  this  faulting  have  been  planed  down  by  glacial 


erosion. 


ORIGIN    OF    LEADVILLE   ORE   DEPOSITS. 


The  ores  are  deposited  for  the  most  part  in  the  blue 
limestone  of  the  Lower  Carboniferous.  As  the  ores  were 
deposited  by  water  solutions,  the  soluble  limestone  beds 
would  be  more  easily  acted  upon  by  solutions  than  the 
sandstones  and  shales  composing  the  other  rocks  of  the 
neighborhood,  which  are  less  susceptible  to  percolating 
water.  The  Paleozoic  frrmations  in  America  are  the  prin- 
cipal repositories  for  lead  and  silver  ores,  not  by  reason 
of  their  geological  age,  so  much  as  by  their  containing  such 
a  quantity  of  soluble  limestone  and  being  physically  as 
well  as  chemically  favorable  for  the  reception  of  mineral 
solutions. 

The  physical  Ptructural  conditions  of  Leadville  are  par- 
ticularly favorable  to  the  concentration  of  percolating  waters 
in  the  blue  limestone.  Great  intrusive  sheets  of  porphyry 
follow  the  limestone  persistently,  principally  on  its  upper 
surface.  This  porphyry  is  very  porous,  and  full  of  cracks 
and  joints,  affording  ready  channels  for  water  from  above, 
and  also  channels  for  ascending  water  from  below,  along 
the  walls  of  the  fissures,  through  which  it  is  erupted.  Such 
waters  passing  through  a  medium  of  different  composition 
would  be  ready  for  a  chemical  interchange  with  the  lime- 
stone. 


m 


iff 


COMPOSITION  OF  ORES. 

The  ores  were  deposited  originally  as  sulphides.  This 
is  shown  by  the  fact  that  the  oxidized  ores  near  the  sur- 
face pass  down  with  depth  into  sulphides.  In  Ten-Mile 
district  these  oxidized  ores  are  seen  to  result  from  the 
alteration  of  a  mixture  of  galena,  pyrite,  and  zinc-blende. 
There  is  very  little  gold  in  the  average  Leadville  ores; 
what  little  there  is  comes  from  the  Florence  mine  (native 
gold),  and  from  others  where  it  is  associated  with  pyrites. 
It  is  usually  associated  with  porphyry  rocks,  and  a  porphyry 
commonly  called  pyritiferous  porphyry  shows  gold  to  exist 
diffused  through  the  pyrites  disseminated  through  its  mass. 

Silver  occurs  as  chloride,  a  secondary  condition,  its  ori- 
ginal condition  probably  being  sulphide. 

Lead  occurs  as  carbonate  and  sulphate  and,  deep  in  the 
mines,  as  sulphide.  Specimens  are  common  of  galena 
nodules  surrounded  by  a  thin  coat  of  sulphate,  and  that 
again  by  a  coat  of  carbonate,  showing  the  order  of  transi- 
tion from  sulphide  to  sulphate  and  thence  to  carbonate. 

In  the  iron  mine  native  sulphur  occurs  as  an  alteration 
product  of  galena. 

Iron  and  manganese  constitute  rather  a  gangue  material 
than  an  ore.  They  are  hydrated  oxides  and  protoxides. 
The  iron  was  originally  deposited  as  sulphide  or  pyrites, 
but  has  been  wholly  transformed  by  oxidation. 

Zinc  is  not  common,  but  occurs  as  calamine  (zir.c  silicate) 
in  needle-like  hairs  and  white  crystals  in  caviiie.s  in  the 
mines.  Its  original  form  was  zinc-blende  (zinc  sulphide), 
as  shov.T  in  the  Ten-Mile  district. 

The  earthy  minerals,  alumina,  lime,  silica  and  magnesia, 
are  in  fair  proportions,  as  might  be  expected  from  ores 
which  are  a  replacement  of  limestone  in  close  connection 
with  poiphyry.  The  alktrline  element  among  the  ores 
might  also  be  traced  to  the  influence  of  the  latter  rock. 

The  agents  of  alteration  were  surface  waters,  which  con- 
tain everywhere  carbonic  acid,  oxygen,  organic  matter, 
chloride  of  sodium  (common  salii,  and  phosphoric  acid. 
The  rocks  through  which  these  waters  passed,  bucb  as  por- 
phyries and  limestones,  were  found  to  contain  phosphoric 
acid  and  chlorine,  while  organic  matter  exists  in  the  blue 


»73 

limestones;  atid  in  the  overlying  shales  and  sandstones  arc 
many  carbonaceous  beds  and  even  beds  of  coal.  Water 
passing  through  these  rocks  would  take  up  all  these  ele- 
ments and  be  ready  for  chemical  reactions. 

Galena  (lead  sulphide)  is  much  richer  in  silver  than  its 
alteration  product,  carbonate  of  lead,  or  cerussite.  On  Car- 
bonate Hill  the  carbonate  averages  40  oz.  silver,  the  galena 
is  145  oz.  to  the  ton.     But  galena  is  harder  of  treatment. 

Silver  is  found  at  times  disseminated  througli  vein  matter 
and  country  rock,  without  the  presence  of  lead,  proving 
that  during  alteration,  silver  was  removed  farther  from  its 
original  condition  and  more  widely  disseminated  than  lead. 

Outcrop  deposits  have  proved  in  many  cases  richer  than 
those  at  depth.  The  deposits  near  the  surface  have  been 
the  refined,  concentrated  remains  of  larger  bodes  gradually 
removed  by  erosion,  as  the  alteration  by  surface  waters 
went  on.  The  baser  and  more  soluble  metals  have  thus 
been  removed  in  solutions,  leaving  behind  the  more  valu- 
able and  perhaps  less  soluble  metals  in  new  and  richer 
secondary  combinations. 

" Kaolin'  or  "  Chinese  talc,"  which  occurs  both  along  the 
line  of  contact  and  between  the  porphyry  and  limestone 
and  also  in  the  heart  of  the  ore  deposit,  is  a  decomposition 
product  from  porphyry.  It  consists  principally  of  hydrated 
silicate  of  alumina  derived  from  the  feldspars  of  the  por- 
phyries, perhaps  at  the  time  when  acted  upon  by  sulphurous 
waters,  which  brought  in  the  original  ore  deposits. 

Calcite  occurs  incrusting  recent  jrevices  and  lining  recent 
cavities. 

Barite  is  common,  generally  associated  with  chloride  of 
sih'er  and  manganese,  and  is  locally  recognized  as  a  sign  of 
rich  ore. 


MODE   OF  FORMATION    OF    LEADVILLE   ORE    DEPOSITS. 

The  ores  were  deposited  from  water  solutions  by  a  meta- 
somatic  interchange,  i.e.,  substance  exchanged  for  substance 
with  the  limestone ;  and  lastly  or  originally  as  sulphides. 

Mineral  matter  is  carried  from  one  place  to  another  within 
the  earth's  crust  by  heat  and  water,  or  these  combined. 
Metasomatic  interchange  of  metal  for  limestone  and  the 
removal  of  dolomite  could  only  have  been  produced   by 


T74 


I 


The  ores  were  not  deposited  i, 
a  replacement  of  the  country 


pr(-t\istin,i^'  rarities, 
rock,  i.e.,  dolomitic 


water, 
but  are 
limestone. 

The  ores  grade  off  gradually  into  the  material  of  the 
limestone,  with  a  definite  limit,  as  would  not  have  been  the 
case  if  the  limestone  had  been  previously  caverned.  The 
only  limiting  outline  to  the  ore  bodies  is  that  formed  by 
the  contact  porphyry. 

Fragments  of  unaltered  limestone  are  found  entirely  en- 
closed within  the  ore  bodies,  and  ore  bodies  often  occupy 
the  entire  space  for  long  distances  between  two  horizontal 
sheets  of  porphyry,  which  space  further  on  is  occupied  by 
the  limestone.  This  is  well  seen  in  Colonel  Seller's  mine. 
Examination  of  ores  and  veinstone  shows  lime  and  magne- 
sia not  in  the  crystalline  condition  they  would  have,  had 
they  been  brought  into  a  pre-existing  cavity  and  deposited, 
but  in  the  same  granular  condition  in  which  they  exist  in 
the  country  rock. 

The  deposits  in  rocks  other  than  limestone  consist  of  me- 
tallic materials  and  of  altered  portions  of  the  country  rock, 
in  which  the  structure  of  the  latter  can  sometimes  be  still 
traced,  and  are  not  the  regular  layers  of  matter  foreign  to 
the  country  rock,  which  results  from  the  filling  of  a  pre- 
existing fissure  or  cavity  by  materials  brought  in  from  a 
distance  and  deposited  along  the  walls. 

In  the  Ten-Mile  district  the  arrangement  of  the  particles 
of  the  original  rock  is  frequently  seen  to  be  preserved  in 
the  metallic  minerals,  which  maintain  a  certain  parallelism 
with  the  original  bedding  planes  in  the  lines  defined  by 
minute  changes  in  these  minerals. 

The  common  characteristic  of  caves  which  have  been 
dissolved  out  of  limestone  is,  that  their  wails  are  coated 
with  a  layer  of  clay  which  has  been  left  undissolved  by  the 
percolating  waters,  and  these  walls  have  a  peculiar  surface 
of  little  cup-shaped  irregularities  from  which  also  stalac- 
tites frequently  hang.  There  is  also  an  accumulation  at 
the  bottom  of  the  cave  of  fragments  of  limestone,  fallen 
from  the  sides  of  the  roof.  None  of  these  characteristics 
are  found  associated  with  the  ore  replacements. 

Also,  when  mineral  matter  is  deposited  in  "  pre-existing 
cavities "  it  takes  the  form  of  regular  layers  parallel  with 
the  walls  of  the  cavity,  as  is  beautifully  shown  in  geodes 


75 


I 


lined  with  a  succession  of  zeolites  or  with  layers  of  chalced- 
ony,  opal  and  quartz. 

No  such  successive  arrangement  in  layers  is  found  in  the 
Leadville  ore  bodies. 

Again,  could  such  large,  open  cavities  have  existed  for 
long  distances  without  support  between  the  layers  of 
porphyry?  Why  did  not  these  porphyry  sheets  close  to- 
gether? And  further,  how  could  such  extensive  cavities 
have  been  formed  and  kept  open  under  a  pressure  of  lo.ooo 
feet  of  rock,  which  the  geology  of  the  region  shows  to  have 
existed  above  the  deposits  at  the  time  they  were  being 
formed?  Such  cavities  as  we  do  find  in  the  region  are  all 
of  very  recent  origin,  cutting  through  both  limestone  and 
ore  bodies,  and  have  been  hollowed  out  by  surface  waters 
more  recent  even  than  those  which  produced  the  secondary 
alterations  in  the  ore  bodies. 

The  ore  deposits  of  Ten-Mile  district  about  Kokomo, 
not  far  north  from  Leadville,  are  very  similar  in  character 
to  those  of  Leadville.  They  occur,  however,  in  a  some- 
what higher  division  of  the  Carboniferous,  and  the  ores  as 
a  rule  are  not  so  decomposed  and  oxidized,  and  the  transi- 
tion from  the  original  sulphide  character  of  the  deposits  to 
the  oxidized  condition  is  more  easily  show"*; 

RED   CLIFF   OOI-n   1»KP()SITS. 

At  Red  Cliff,  still  further  north  of  Leadville,  in  the  val- 
ley of  the  Eagle,  the  same  geolc%ic  series  are  found,  pene- 
trated, as  at  Leadville  an<d  Kokomo,  by  eruptive  sheets. 
In  the  limestones  at  contact  with  the  porphyries,  much  the 
same  classes  of  ore  »lepv>sits  occur,  but  the  peculiar  and  in- 
structive feature  of  tiie  jamp  is  the  rich  deposits  of  gold  in 
chambers  and  cavities  in  the  hard  and  usually  unproductive 
Cambrian  quartzites  resting  on  the  granite. 

The  gold  in  these  chambeis  often  occurs  as  nuggets. 
The  quartzites  dip  about  lo^  N.  E.,  and  between  their  bed- 
ding planes  lies  the  ore.  The  so-called  contact  or  bedding 
plane  between  one  stratum  of  quartzite  and  another  is 
clearly  defined.  At  this  line  there  is  a  filling  so  to  speak 
of  "  brecciated,"  broken  up  quartzite  fragments  cemented 
by  iron  rust  and  at  times  by  iron  pyrit**  Thu  thickness  of 
this  breccia  varies  between  four  and  six  feet.  Ore  chim- 
neys on  this  breccia  occur  at  mtervali, 


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176 


Their  presence  is  indicated  on  the  outcrop  by  seams  of 
rusty  clay,  which  lies  on  top  of  the  ore  body  and  follows  it 
along  the  roof  of  the  deposit  for  100  to  200  feet,  then  thins 
out  gradually  and  disappears  entirely;  at  the  point  of  its 
disappearance,  unaltered  iron  pyrites  set  in. 

These  ore  chimneys  are  about  4  feet  in  width,  their  thick- 
ness is  limited  to  the  space  between  the  floor  and  roof. 
The  quartzite  roof  is  always  smooth,  but  the  lower  quartz- 
ite  floor  is  rough  and  corrugated  and  shows  chemical  action 
on  it  attendant  on  deposition  of  ore.  The  floor  at  times  is 
impregnated  with  ore,  which  does  not,  however,  extend  any 
great  distance  into  it.  Though  the  ore  chimneys  are  from 
4  to  6  feet  wide  the  pay  ore  is  only  a  few  inches,  swelling 
form  floor  to  roof.  The  pay  ore  in  the  oxidized  rusty  por- 
tion yields  7  ounces  gold  and  50  ounces  silver. 

In  mining,  the  floor  is  followed  as  a  guide.  Individual 
ore  chimneys  are  connected  laterally  by  ore  chutes  like  a 
network.  These  ore  chimneys  divide  and  separate,  the 
branches  reuniting  or  again  splitting  up.  The  whole  rami- 
fication conies  together  again  at  intervals  in  one  main 
chimney.  The  rock  filling  the  space  where  the  divergence 
has  taken  place  is  the  same  as  the  breccia  filling,  only  more 
compact  and  impregnated  with  pyrite.  These  fillings  are 
left  standing  as  pillars  after  the  ore  is  mined. 

To  sum  up,  the  characteristics  of  these  deposits  are : 

First.  The  outcrop  of  the  ore  chimney  indicated  by 
what  is  locally  called  a  "  joint-clay." 

Second.  A  zone  of  oxidation  for  200  feet,  which  grad- 
ually merges,  as  the  natural  water  level  is  approached, 
through  a  zone  of  mixed  oxides  and  sulphides  to  the  zone 
^f  unaffected  sulphides. 

Third.  The  "joint-clay"  gradually  disappears  as  the 
sulphides  are  approached.  The  ore  on  analysis  shows  ses- 
quioAide  and  sesquisulphate  of  iron,  silica  and  alumina, 
and  sulphate  of  barium. 

In  the  Ground  Hog  mine  the  ore  chimneys  are  600  feet 
apart,  but  are  probably  connected.  They  abound  in  nug- 
gets ;  the  latter  are  sometimes  twiated  like  bent  horns ;  in 
other  chutes  they  are  lumpy,  composed  of  crystalline  gold 
particles  cemented  together  by  sesquisulphate  of  iron  and 
horn  silver. 

Nuggets  are  found  in  troughs  in  the  quartzite  floor  ini- 


^77 

bedded  in  clay  associated  with  rich  silver  or  horn  silver 
ore.  With  the  nuggets  are  lumps  of  sesquisulphate  of  iron 
carrying  much  gold.  This  proves,  according  to  Mr.  Ciui- 
terman,  that  the  secondary  deposition  of  gold  in  crystals 
was  through  the  medium  of  persulphate  of  iron  derived 
from  slow  xidation  of  iron  pyrites,  and  is  an  admirable 
confirmation  of  the  theory  as  stated  by  Prof.  Le  Conte  in 
his  geology. 

ASPEN    ORE    DEPOSITS, 


The  Aspen  mining  region  is  geologically  related  to  that 
of  Leadville;  each  is  on  the  shore  line  of  the  old  Archwan 
island  of  the  Sawatch,  one  on  the  east,  the  other  on  the 
west,  opposite  one  another,  but  about  50  miles  apart. 

The  ore  deposits  occur  in  the  same  general  horizon,  viz., 
the  Lower  Carboniferous. 

Both  regions  show  intense  disturbance,  both  by  volcanic 
intrusions  of  igneous  rock,  folding,  and  faulting.  The 
process  of  ore  deposition  in  both  regions  has  been  an  ac- 
tual replacement  of  the  country  rock  by  vein  material. 

At  Aspen  the  ore  is  not  found  in  actual  contact  with  the 
overlying  eruptive  igneous  rock,  but  at  some  depth  down 
in  the  limestone,  at  a  zone  where  the  "  blue  limestone"  be- 
comes dolomized,  or,  as  Aspen  miners  say,  "  passes  from 
blue  lime  into  short  lime." 

The  mines  of  Aspen  are  situated  in  Paleozoic  strata  re- 
clining upon  the  slope  of  a  narrow  ridged  mountain,  form- 
ing a  granite  spur  "  en  echelon"  with  the  Sawatch  range. 

The  strip  of  '^untry  in  the  vicinity  of  Aspen  constitutes 
the  dividing  li..  between  the  two  distinct  uplifts  of  the 
Sawatch  range  on  the  east,  and  the  Elk  mountains  on  the 
west,  and  has  been  successively  affected  by  each  upheaval. 

The  Sawatch  upheaval  was  a  gradual  elevation  of  this 
mountain  mass  resulting  from  a  gradual  subsidence  of  the 
adjoining  sea  bottoms,  which  caused  the  sedimentary  beds 
deposited  in  those  sea  bottoms  to  slope  up  at  varying 
angles  all  along  the  ancient  shore  line  toward  the  central 
mass  of  the  Archaean  island. 

The  Elk  Mountain  range,  which  extends  to  the  west  and 
south  of  this  region,  was  upheaved  later  than  the  Sawatch, 
with  greater  violence  and  eruptive  energy,  and  the  up- 

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heaval  was  accompanied  by  enormous 
intrusions  of  eruptive  rock  which 
were  forced  into  the  sedimentary 
strata  already  shattered  by  the  forces 
of  upheaval,  in  great  "  laccolites,"  or 
solid  masses,  and  spread  out  through 
them  in  every  direction  in  the  form 
of  dykes  and  intrusive  sheets.  The 
surface  'ixposures  of  these  igneous 
bodies  cover  areas  of  twenty-five  to 
thirty  square  miles,  and  their  exten- 
sion below  the  surface  is  doubtless 
very  much  greater. 

The  intrusion  of  such  enormous 
masses  of  foreign  matter  must  not 
only  have  gp*eatly  disturbed  the  beds 
within  the  region  of  upheaval,  but 
also  have  so  expanded  the  volume 
of  the  earth's  crust  in  this  area  as 
to  cause  a  severe  lateral  pressure  in 
the  adjoining  region.  That  adjoining 
region  was  Aspen  and  its  neighbor- 
hood. 

It  would  be  just  in  the  strip  of 
sedimentary  beds  along  the  Aspen 
Mountain  ridge,  which  is  backed  by 
a  projecting  point  of  the  unyielding 
Sawatch  Archaean,  that  this  compres- 
sion would  be  most  severely  felt,  the 
Sawatch  granite  mass  acting  as  a 
point  of  resistance  against  the  in- 
tense lateral  compression  caused  by 
the  younger  Elk  Mountain  uplift. 

The  sedimentary  beds  resting 
against  the  Archaean  correspond  gen- 
erally, with  slight  differences,  to  those 
in  the  South  Park  and  Leadville  re- 
gion in  a  similar  position. 

The  latter  were  deposited  in  a 
partially  enclosed  bay,  now  consti- 
tuting the  South  Park  basin,  the  form- 
er on  the  west  side  of  the  Archaean 


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island  in  a  wider  and  deeper  sea.  and  on  this  western  slope 
the  beds  are  generally  much  thicker  than  those  of  corre- 
sponding geological  horizons  on  the  east. 


STRATIGRAPHY    OF   ASPEN. 


:         / 


1.  The  horizons  represented  are  the  Upper  Cambrian 
quartzites,  200  feet,  resting  on  the  Archaean  granite. 

2.  Silurian  silicious  limestones  and  quartzites,  340  feet. 

3.  Darker  limestones,  rusty  brown  and  dolomitic  at  base, 
blue  compact  and  pure  on  top,  240  feet.  (These  are  Lower 
Carboniferous.) 

4.  Carboniferous  clays  and  shales  and  thin  bedded  lime- 
stones, 425  feet.  These  belong  to  the  Weber  grits  (Middle 
Carboniferous). 

5.  A  series  of  variegated  green  and  red  sandstones,  clays 
and  shales,  some  limestones  and  red  sandstones  of  the 
Upper  Carboniferous. 

6.  Heavy  bedded  red  sandstones  (Triassic). 

Above  these  again  are  several  thousand  feet  of  Creta- 
ceous strata,  up  to  the  base  of  the  Laramie  coal  beds. 
(The  Cretaceous,  however,  and  the  Jurassic  do  not  rest  im- 
mediately upon  the  granite). 

Diorite. — On  Aspen  Mountain  is  a  bed  of  "  white  por- 
phyry" (diorite)  in  the  black  shales,  60  to  100  feet  above 
the  top  of  the  blue  limestone.  It  is  260  feet  thick  on  the 
slope  back  of  town,  but  thickens  considerably  to  the  south, 
and  is  traceable  to  Ashcroft.  It  appears  to  extend  also 
across  the  valley  of  Roaring  Fork  to  Smuggler  Mountain. 
Small  intrusive  sheets  also  occur  in  the  lower  quartzites 
near  the  point  of  Aspen  Mountain  and  on  the  east  face  of 
Richmond  Hill. 

As  affected  by  the  Sawatch  upheaval,  these  beds  wrap 
around  the  Archaean  mass,  resting  against  or  dipping  away 
from  it  at  varying  angles. 

The  quartzites  and  limestones  cross  the  valley  of  Roaring 
Fork  from  Smuggler  Mountain  to  Aspen  Mountain,  striking 
northeast  and  southwest,  dipping  northwest.  The  angle 
of  dip  is  about  45°,  varying  from  a  minimum  of  30°  to  a 
maximum  of  60°  in  "  flats"  and  "  steeps." 


i8i 


THE   ORE   BODIES. 

The  Lower  Carboniferous  "  blue  limestone"  is  compact, 
homogeneous  and  composed  of  pure  carbonate  of  lime.  The 
"  brown"  or  "  short"  dolomitic  limestone  is  of  a  dark  gray 
color,  finely  crystalline,  finely  granulated  and  traversed  in 
every  direction  by  a  network  of  minute  veinlets  containing 
iron  salts,  wiiich,  when  oxidized,  color  the  surface  a  rusty 
brown.  The  c  xidation  along  these  minute  veins  makes  the 
rock  break  easiily  into  dice-shaped  fragments  giving  the 
rock  a"crackjy"  striicture,  hence  its  local  name  of  short 
lime. 

Ore  Distnbution. — The  outlines  of  the  ore  bodies  cannot 
be  detected  by  the  eye,  owing  to  the  gradual  transition 
from  ore  to  country  rock. 

The  o'/e  is  not  confined  to  the  brown  dolomite  below  the 
so-called  contact,  but  several  ore  bodies  extend  20  or  30 
feet  above  this  contact  into  the  blue  limestone  and  in  some 
cases  follow  the  lines  of  cross-fracture  entirely  across  the 
blue  limestone. 

The  ore  is  not  confined,  either,  to  a  definite  plane  or  con- 
tact between  two  dissimilar  beds  of  limestone  and  dolomite 
from  which  its  solutions  have  eaten  into  the  underlying 
dolomite,  for  in  the  first  place  there  is  not  one  single  con- 
tact, but  many ;  and  if  this  so-called  contact  constitutes  an 
essential  condition  of  ore  deposition,  there  is  no  reason 
why  it  should  be  confined  to  the  one  and  not  found  in  the 
others  where  the  rocks  have  the  same  composition. 
Again,  ore-bearing  solutions  would  not  be  likely  to  eat  up- 
wards for  any  great  distance  from  the  contact  plane  if  they 
entered  the  beds  along  this  plane. 

This  so-called  contact  plane  is  well  defined  on  Spar 
Ridge  and  continues  down  with  the  dip  in  the  underground 
working,  but  ore  bodies  occur  above  and  below  it. 

The  rock  thus  mineralized  is  dolomite  in  most  cases,  but 
it  is  none  the  less  above  the  true  bedding  plane  called  the 
contact. 

In  other  parts  there  has  been  fracturing  across  the  beds 
as  shown  by  a  vertical  breccia  of  limestone  fragments  with 
a  cement  of  iron  oxide  and  manganese. 

Over  the  ore  bodies  are  lines  of  open  cavities  following 


l82 


the  lines  of  cross-fracture,  through  which  the  ore  solutions 
passed  which  deposited  the  ore  bodies.  These  caves  are 
now  being  hollowed  out  by  water  descending  from  the  sur- 
face dissolving  the  limestone  in  the  roof  and  flowing  off 
along  the  floor,  depositing  a  mud  of  silica,  alumina,  lime, 
magnesia  and  iron  oxide. 

Hence  this  contact  is  not  necessarily  the  only  ore  channel 
of  the  district,  and  other  channels  may  be  sought  for. 

Portions  of  the  ore  bodies  have  been  formea  by  solutions 
percolating  through  cross-fractures  and  spreading  out  be- 
tween the  parallel  bedding  planes. 

This  would  happen  if  these  solutions  derived  their  met- 
als from  the  overlying  porphyry,  for  it  is  separated  from 
the  limestone  by  argillaceous  shales  which  would  be  im- 
pervious unless  fractured  across  the  bedding.  The  analy- 
sis of  the  lime  mud  at  bottom  of  the  cave  shows  by  its 
preponderance  of  alkalies,  which  do  not  exist  in  the  com- 
position of  either  brown  or  blue  limestone,  that  the  waters 
dissolving  it  came  from  the  porphyry.  The  waters  brought 
both  alkalies  and  silica  from  the  porphyry,  and  probably  the 
iron  and  baryta. 

DOLOMITIZATION. 

This  is  a  secondary  process  upon  the  blue  limestone  by 
magnesian  waters,  which  is  proved  by  irregular  tongues  of 
dolomite  extending  up,  into  and  across  the  blue  limestone. 
The  lenticular  bodies  in  the  Durant  cliff  point  to  the  same 
fact.  The  crackly  structure  of  the  brown  lime  results  from 
the  replacement  of  a  molecule  of  lime  by  a  molecule  of 
magnesia,  involving  also  a  contraction  in  volume  of  the 
rock  itself,  which  would  cause  it  to  separate  in  angular 
fragments,  the  intersections  filled  by  material  more  solu- 
ble than  the  rock  itself. 

The  magnesian  waters  may  have  been  connected  with 
those  which  brought  in  the  vein  materials. 

In  the  ore  bodies  the  partially  mineralized  rock  on  the 
borders  of  the  ore  is  changed  to  dolomite,  hence  dolomiti- 
zation  either  preceded  or  accompanied  ore  deposition. 

Mr.  Emmons  suggests  as  probabilities  only,  that  the  por- 
phyry intrusion  preceded  the  faulting ; 

That  the  ore  deposit  followed  the  intrusion  of  porphyry 
fUid  also  the  principal  faulting  movements ; 


1 83 

That  small  movements  have  taken  place  in  recent  times 
both  in  the  strata  and  contained  ore  bodies  since  the  oxida- 
tion of  the  latter ;  that  at  the  time  of  the  great  faulting,  the 
beds  may  not  have  attained  entirely  their  present  position. 

In  the  vicinity  of  Aspen  Mountain  ore  bodies,  the  strata 
appear  to  have  been  synclinally  folded  and  faulted  between 
the  main  Archaean  area  on  the  east,  and  a  mass  of  granite 
at  the  western  extremity  of  the  mountain,  thus  producing  a 
second  series  of  oppositely  inclined  beds,  also  containing  a 
few  ore  bodies.  Intrusions  of  altered  eruptive  diorite  oc- 
cupy a  prominent  position  in  the  intervening  trough  and 
may  have  seriously  faulted  or  dislocated  the  strata  in  the 
depths.  The  bulk  of  the  Aspen  ores  are  largely  oxidation 
products  of  argentiferous  minerals  with  true  silver  miner- 
als, associated  with  calcspar  and  baryta;  it  is  a  "dry  ore" 
requiring  to  be  mixed  with  silicious  lead  ores  before  it 
can  be  treated.  Such  rich  ores  as  polybasite  and  brittle 
silver  occur  also. 

A  great  deal  of  the  ore  consists  of  fine  grained  steel  ga- 
lena, very  rich  in  silver. 


ASPEN    AS   A    PROSPECTING   GROUND. 

Aspen  again  is  an  example  of  a  region  that  had  often 
been  skimmed  over  by  the  prospector  and  abandoned  be- 
fore the  final  thorough  prospecting  revealed  its  great 
riches.  Years  ago  some  prospectors  found  signs  of  "  float" 
and  "  blossom"  cropping  out  under  the  blue  limestone  of 
Spar  Ridge.  They  even  went  so  far  as  to  sink  an  incline 
of  a  hundred  feet  or  more,  but  though  they  found  ore,  its 
character  was  so  low  grade,  that  the  mine  was  for  a  long 
time  shut  down  and  practically  abandoned.  Then  an  en- 
terprising individual  conceived  the  idea  of  boring  down  on 
the  sloping  back  of  the  limestone  in  the  adjoining  Vallejo 
gulch,  to  tap  the  ore  body,  already  discovered  along  the 
outcropping,  on  the  underside  of  the  limestone.  At  about 
50  feet  deep  the  limestone  was  pierced,  and  an  enormously 
large  and  rich  ore  body  was  discovered.  Immediately  the 
original  locators  began  again  with  all  speed  to  push  on 
their  incline,  and  then  originated  the  celebrated  "  apex  and 
side  line"  lawsuit.  The  original  locators  had  the  apex  on 
the  outcrop.     They  therefore  claimed  the  whole  mountain, 


i84 

and  tried  to  drive  out  the  side  line  men.  Finally  a  com- 
promise was  effected,  but  that  boring  down  on  the  back  of 
the  limestone  and  its  discoveries  led  immediately  to  an 
army  of  prospectors  examining  the  mountain,  and  it  was 
astonishing  how  many  ore  deposits  were  discovered  in  a 
region  that  was  supposed  to  have  been  prospected  and 
given  up  as  no  good.  Of  course  Aspen  is  an  example  of 
"  richness  with  depth."  A  dangerous  precedent  and  en- 
couragement to  that  often  ruinous  policy  of  running  long 
cross-cut  tunnels  to  cut  an  ore  body  at  depth,  which  has 
only  proved  indifferently  good  near  the  surface,  on  the 
fallacy  we  have  before  alluded  to,  of  the  improbable  prob- 
ability of  "  richness  increasing  with  depth." 

AN    EXAMPLE  OF   PROSPECTING. 

Now  supposing  our  prospector  was  the  first  man  to 
enter  that  legion  years  ago.  What  signs  were  there  to 
lead  him  to  think  it  was  a  good  prospecting  ground?  Sup- 
posing him  to  be  fairly  versed  in  geology,  he  would  have 
noticed,  as  he  came  down  over  the  Sawatch  range,  that 
the  Paleozoic  strata  he  had  observed  as  ore-bearing  at 
Leadville,  out-cropped  also  on  this  western  side,  together 
with  the  "  blue  limestone ;"  secondly,  he  would  have  no- 
ticed the  presence  of  large  masses  of  eruptive  rock  consti- 
tuting the  Elk  range ;  thirdly,  he  would  observe  the  region 
was  much  disturbed,  that  the  strata  were  intensely  folded, 
and  intensely  faulted.  All  these  signs  he  would  have  con- 
sidered likely.  Then  after  following  up  the  various 
creeks,  he  would  select  such  spots  as  where  he  saw  the 
massive  blue  limestone  outcropping.  He  would  readily 
find  this  bed  from  its  relation  to  the  ^amie  and  Cambrian 
quartzite  belov/.  He  would  look  for  places  where  por- 
phyry was  intruded  into  the  limestone  or  where  great 
masses  of  it  lay  above  or  in  vicinity  of  the  limestone. 
This  would  probably  have  led  him,  on  nearing  Aspen 
Mountain,  to  give  that  mountain  more  than  a  passing  look. 
He  would  notice  that  the  strata  on  Aspen  Mountain  were 
very  much  disturbed  and  faulted,  that  a  spur  of  granite, 
quite  out  of  place,  came  right  up  through  the  middle  of 
the  mountain,  that  strata  were  pitching  in  various  direc- 
tions off  from  this,  and  moreover  that  in  the  lap  of  this 


I 


fault-fold  was  a  very  thick  bed  of  porphyry.  He  would 
observe  the  line  of  change  from  the  blue  limestone  to  the 
dolomite,  and  at  that  line  he  would  have  prospected  and 
found  and  followed  up  the  "  blossom"  at  the  line,  consisting 
of  calcite  and  baryta  running  in  a  rusty  line,  like  the  out- 
crop of  a  coal  seam,  all  up  the  side  of  Spar  Gulch,  and  so 
he  would  have  discovered  the  great  Aspen  ore-deposits, 
and  by  following  up  the  indications  along  the  outcrop  and 
locating  claim  after  claim  as  along  an  outcropping  coal 
seam,  he  could  have  secured  practically  the  whole  "apex" 
of  the  hill,  and  become  master  of  the  mountain  and  all  it 
contained ;  but  had  he  known  then  the  litigation  of  "  side 
line  and  apex"  that  was  to  arise,  he  should  have  gone 
further,  and  located  claims  covering  the  side  line,  on  the 
back  of  the  sloping  limestone  ridge,  leading  down  into 
Vallejo  gulch.  But  again  he  might,  like  the  original  first 
discoverers,  have  become  disheartened  with  his  find  on 
testing  the  outcropping  ore  by  assay  or  mill-run,  and  find- 
ing it  so  low  grade  near  the  surface.  On  general  principles 
in  this  respect  he  would  have  been  right. 

Now  having  thoroughly  explored  the  little  Aspen  Moun- 
tain, he  would  observe  that  much  the  same  formations 
crossed  the  creek  and  entered  into  Smuggler  Mountain, 
though  much  obscured  by  heavy  glacial  drift.  Here  he 
might  have  located  fresh  claims  on  this  hill,  and  become 
the  owner  of  the  celebrated  Smuggler,  Regent  and  other 
mines  with  their  untold  wealth.  Thence  he  might  have 
continued  his  successful  trip,  and  followed  the  same  so- 
called  "  contact"  outcrop  for  miles  on  to  Ashcroft.  It  must 
be  remembered  here,  however,  that  in  locating  all  these 
claims,  whilst  the  prospector  may  drive  his  location  stake 
at  every  1,500  feet,  he  is  required,  within  sixty  days  after 
location,  to  dig  a  ten-foot  hole  in  each  location.  As  this 
may  be  a  little  difficult  for  him  to  do  he  generally  enlists 
others  in  his  enterprise,  to  assist  him,  and  enters  some  of 
the  claims  in  their  names,  to  prevent  the  discoveries  being 
jumped  by  a  horde  of  prospectors  who  press  in  as  soon  as 
anything  is  found.  Good  advice  to  a  prospector,  is  to  keep 
very  still  and  "  mum"  about  his  discoveries  until  he  has 
well  secured  them,  and  to  be  very  careful  how  he  "  opens 
his  head"  to  any  one.  Commonly  a  prospector  who  has 
"  struck  it, "comes  into  town,  fills  up  with  whiskey.  "  blows 


tm 


1 86 


it  in,"  and  then,  "  blows  it  off"  all  over  town  about  his  dis- 
covery, and  is  elated  to  find  himself  the  hero  of  the  hour. 
The  result  is,  before  daylight  the  following  morning, 
a  hundred  men  are  chasing  one  another  in  the  direction  of 
his  discovery,  and  before  a  day  or  more  is  over,  the  moun- 
tain is  covered  with  locations  as  close  as  graves  in  a  city 
churchyard,  and  in  a  week's  time  these  locations  are  cov- 
ered again  by  a  second  layer,  as  the  saying  is,  "several 
feet  deep." 

A  boom  follows.  The  offscourings  of  the  country  pour 
in  with  the  saloon,  dance  hall  and  gambling  hell  element. 
A  murder  or  two  follows.  Lynch  law  takes  a  hand.  Then 
a  horde  of  real  estate  men  come  in,  and  lots  are  sold  at 
fabulous  prices,  and  the  town  is  inflated  with  a  population 
and  everything  else  usually  far  above  the  capacity  of  the 
mines  to  support.  A  collapse  follows,  and  a  steady  retreat 
of  hollow-eyed,  disappointed  adventur^^rs.  In  time  the 
town  and  camp  assume  their  lawful  proportions  and  busi- 
ness settles  down  to  its  lawful,  regime. 

Whilst  all  this  has  been  going  on,  and  amidst  all  the 
fuss  and  bustle  and  "  hooraying"  of  real  estate  "  boomers" 
and  so  forth,  some  prospectors  have  been  quietly  trying  to 
follow  up  the  first  desirable  indications  into  the  neighbor- 
ing region,  resulting  often  in  an  extension  of  the  ore-bear- 
ing region.  Some  of  these  locations  are  "  bona  fide"  and 
valuable.  Other  "holes  in  the  ground"  are  dug  on  the 
merest  pretext  of  indications  to  catch  the  ignorant,  adven- 
turous tenderfoot  capitalist  purchasers,  or  "suckers."  An 
investor  going  into  the  camp  at  such  a  time  linds  a  fabu- 
lous price  placed  on  every  prospect,  whether  genuine  or 
false.  As  a  prudent  man,  he  either  beats  down  such  prices, 
or  concludes  he  will  visit  the  camp  a  little  later,  when  the 
excitement  and  inflation  has  gone  down,  and  when  things 
are  on  more  of  a  business  footing,  and  something  like,  the 
real  value  of  the  camp  has  been  found  and  proved.  Of 
course  in  such  a  gambling  speculation,  by  such  prudence 
and  delay  he  may  lose  a  lucky  chance,  but  he  has  preserved 
his  prudence  and  escaped  being  wofully  bitten. 

Perhaps,  in  a  month's  time,  the  discoveries  are  found  to 
be  merely  superficial,  the  boom  utterly  collapses,  and  the 
dreary  sight  is  seen  a  little  later,  of  a  desolate  village, 
with  frame  houses  and  log  cabins,  and  possibly  a  mill  or 


i87 

two,  for  mills  are  sure  to  follow,  lying  in  wreck  and  ruin, 
a  home  for  the  owls  and  the  bats:  or  else  the  genuine  dis- 
CO  very  produces  one  or  two  mines  and  supports  a  handful 
of  population  legitimately. 

Again,  a  region  like  Aspen  may  disclose  a  limited  num- 
ber of  very  rich  ore  deposits,  but  sufficient  to  support  and 
sustain  a  fair  sized  town. 

But  the  most  important  and  most  lasting  discoveries  of 
all  are  of  areas  producing  an  immense  quantity  of  low 
grade  ore  such  as  Leadville.  This  gives  an  opportunity 
for  a  great  number  of  mines  and  for  the  support  of  a  large 
and  permanent  town. 


CHAPTER  XIII. 


EXAMINING    AND    SAMPLING    MINING   PROPERTIES. 
PROSPECTS  OR  MINES. 

A  prospector  may  be,  or  become,  a  "  mining  expert"  and 
be  called  upon  to  make  examinations  of  mining  properties, 
whether  prospects  or  developed  mines,  so  a  few  sugges- 
tions may  prove  useful. 

Mining  properties  of  the  precious  metals  are  generally  of 
two  kinds,  those  containing  ore  deposits  in  place,  such  as 
fissure  veins  and  blanket  deposits  and  placers,  the  latter 
being  gold-bearing.  In  both  cases,  and  especially  in  the 
former,  the  character,  position  and  other  relations  of  prop- 
erties are  infinitely  varied,  so  that  no  hard  and  fast  rule  can 
be  given  to  suit  all  cases;  certain  rules,  however,  will  gen- 
erally apply. 

A  mining  engineer  receives  a  letter  from  a  company  tell- 
ing him  to  go  to  such  and  such  a  country  or  region  and 
examine  and  report  on  a  certain  property  that  has  been 
offered  them.  Such  a  mandate  is  usually  accompanied  by 
a  letter  or  report  from  the  owner  or  parties  offering  the 
property,  giving  the  owner's  description  of  the  same,  or 
else  the  report  of  some  expert  on  it.  As  a  general  rule 
such  reports  give  the  most  favorable  view,  and  in  some 
cases  must  be  taken  "cum  grano  salts."  To  the  mining 
engineer  they  give  some  sort  of  an  ider,  as  to  what  the 


1 88 


property  maybe  like.  Ah  to  its  value,  etc.,  that  he  pro- 
poses to  find  out  for  himself.  The  company  sometimes 
asks  him  to  examine  with  a  view  to  verifying  or  modifying 
or  contradicting  such  reports. 

The  region,  the  country,  the  character  of  the  deposits, 
the  local  conditions,  may  in  all  probability  be  compara- 
tively new  or  strange  to  him.  Prior  to  starting  he  may 
make  inquiries  in  mining  circles  if  anything  is  known 
about  the  region  or  district.  If  there  are  any  published 
mining  or  geolo^.ical  reports  or  maps,  he  will  consult 
these.  Finally  he  starts  out  with  as  little  baggage  as  pos- 
sible, usually  a  small  hand-bag,  containing  a  few  necessa- 
ries ;  a  tape  line,  geological  pick,  clinometer  and  compass 
and  note  or  sketch  book.  TTis  dress  is  generally  a  suit  of 
corduroys,  leather  gaiters  and  strong  boots. 

As  he  enters  the  region  by  rail  or  on  horseback  he  no- 
tices the  main  geological  features,  whether  the  rocks  are 
granitic,  sedimentary,  or  eruptive.  Finally,  he  reaches  the 
camp,  calls  on  the  owner  or  superintendent,  and  rides  up 
with  him  to  visit  the  mine.  If  he  should  "  lay  over"  for  the 
afternoon  in  the  village,  he  may  as  indirectly  as  possible  try 
to  pick  up  any  gossip  there  may  be  afloat  relating  to  the 
property.  He  is  at  once  impret^sed  with  the  accessibility 
or  inaccessibility  of  the  property,  and  estimates  the  prob- 
able cost  of  bringing  down  the  ore  to  the  mill  or  to  the 
railway  track,  and  observes  the  proximity  or  absence  of 
timber  and  water  power.  At  last  he  reaches  the  mine, 
dines  at  the  boarding  house,  and  is  then  taken  over  the 
premises  by  the  superintendent.  His  first  attention  is  di- 
rected to  the  surface  character  of  the  property,  its  topog- 
raphy, whether  rolling,  smooth  or  precipitous,  whether  it 
is  high  above  the  valley  or  near  down  to  it,  whether  the 
mine  is  high  or  low  as  regards  the  water  level  or  drainage 
system  of  the  neighborhood,  whether  the  property  is  con- 
veniently situated  for  wOik::ig  the  mine  and  transporting 
the  ore.  etc. 

Accessibility  is  an  important  matter.  In  some  regions, 
jiTch  as  in  the  San  Juan  district  (Colorado)  for  example, 
mines  and  prospect  holes  are  sometimes  on  the  top  or  sides 
of  mountains  or  precipices,  thousands  of  feet  above  the 
valley  below,  located  at  spots  one  would  think  only  an 
eagle  could  reach ;  prospect  tunnels,  too,  are  driven  where 


i89 


190 


there  appears  scarcely  a  foothold  for  a  squirrel.  No  spot, 
however,  seems  too  inaccessible  for  the  prospector.  At  a 
glance  the  engineer  sees  that  in  a  property  situated  in 
such  a  region,  accessibility  is  one  of  the  first  and  often  most 
formidable  problems  to  be  considered. 

To  some  of  these  mines  are  long  zigzag  trails  cut  in  the 
side  of  the  mountain.  The  engineer  calculates  how  much 
the  owners  of  the  donkey  or  "  burro"  train  will  charge  to 
bring  that  ore  down  to  the  valley  or  mill.  He  argues  that 
a  mine  at  that  almost  inaccessible  height  ought  to  carry  a- 
good  deal  of  pretty  high  grade  ore  to  pay  even  for  trans- 
portation by  the  "  burros,"  let  alone  the  cost  of  freight 
afterwards  to  distant  smelting  works.  On  the  other  hand 
a  mine  whose  workings  open  out  within  easy  access  of  the 
valley  or  railway  track,  could  afford  to  carry  less  valuable 
ore.  Then  there  is  timber  and  water  power  to  be  consid- 
ered, the  former  for  timbering  the  workings  of  the  mine, 
the  latter  for  running  a  stamp  mill,  or  for  supplying  steam 
power  to  the  engines  of  the  mine.  If  there  be  no  water 
power,  and  the  vein  carries  free  gold,  the  ore  must  be  car- 
ried down  to  the  nearest  stamp  mill.  In  a  young  or  "  vir- 
gin" property  or  prospect,  the  engineer  will  look  out  for  a 
convenient  site  for  such  a  mill,  under  a  developed  p'-op- 
erty ;  if  there  be  a  mill  on  the  premises,  he  will  examine 
and  report  on  its  capacity  and  suitability  for  treating  the 
ores.  A  mill  site  must,  of  course,  be  selected  close  to 
some  water  power.  In  some  districts  there  is  a  super- 
abundance of  water,  in  others  a  serious  lack  of  it,  or  the 
supply  is  meagre  at  certain  seasons,  or  is  frozen  up  in  win- 
ter. Some  mines  are  quite  dry,  but  generally  they  will 
supply  enough  mine-water  from  their  workings  to  afford 
steam  power. 

He  observes  the  character  and  dip  and  direction  of  the 
veins  if  exposed  on  the  surface,  examines  any  prospect 
holes  on  them,  and  takes  a  few  samples  for  assay.  He  will 
consider  the  nature  of  the  ore  deposits,  whether  they  are 
in  fissure  veins  in  crystalline  rocks,  or  blanket  deposits  in 
sedimentary  rocks,  or  contacts  at  junction  with  eruptive 
porphyries.  A  great  variety  of  local  and  minor  details 
have  to  be  noticed  which  can  hardly  be  specified. 

Having  looked  over  the  surface,  he  enters  the  tunnel  or 
workings  with  the  superintendent.     As  he  passes  along. 


191 


6^0  Mm 


the  latter  is  likely  to  call  his  attention  to  this  or  that  apot, 
as  especially  good,  and  naturally  he  rather  overloohs  the 
poorer  parts  of  the  mine.     He  may  suggest  the  aavisabil- 


192 

ity  ot  taking  samples  from  such  favorable  spots.  The  en- 
gineer, however,  takes  little  heed,  as,  if  he  were  to  confine 
his  attention  to,  and  sample  only,  these  choice  portions,  he 
would  obtain  an  incorrect  estimate  of  the  average  run-  of 
the  mine.  Moreover  in  some  cases  it  is  well  to  be  on  the 
lookout,  lest  these  points  to  which  special  attention  is 
called  by  the  miner  be  previously  "  salted"  or  "  prt  up"  for 
the  expert,  and  charged  in  various  ways  by  rich  ore. 

Having  traversed  the  workings  and  obtained  a  general 
idea  of  the  position  of  the  vein  and  ore  bodies,  and  taking 
an  inventory  of  the  amount  of  development,  length  of 
drifts,  shafts,  etc.  (the  latter  he  can  obtain  from  a  map  of 
the  mine  in  the  superintendent's  oflfice,  a  copy  of  which  he 
will  send  to  his  company)  he  asks  the  superintendent  to 
leave  him  and  his  assistant  and  vacate  the  mine,  as  he  doen 
not  wish  any  one  except  his  assistant  to  be  with  him 
whilst  he  is  taking  samples  for  assay. 

SAMPLING.  ^ 

Now  begins  his  hard  and  most  telling  work,  the  time  and 
labor  depending  very  much  upon  the  size  and  amount  of 
development  in  the  mine,  or  the  degree  of  accuracy  neces- 
sary. Taking  a  large  strip  of  muslin,  he  cuts  part  of  it  up 
into  small  pieces  about  the  size  of  a  pocket  handkerchief, 
these  are  to  contain  his  samples  for  assay,  when  quartered. 
Then  he  takes  the  remainder  of  the  muslin,  or  better  still 
an  ordinary  candlebox,  this  to  catch  the  mass  of  small  frag- 
ments he  detaches  from  the  vein  with  his  pick. 

Now  with  a  light  pick  or  with  a  chisel  and  hammer  he 
begins,  either  from  the  entrance  or  end  of  the  tunnel,  to 
detach  small  portions  of  the  rock,  cutting  a  rough  groove 
across  the  ^  ein.  Sometimes  the  tunnel  occupies  the  whole 
width  of  the  vein,  in  which  case  he  will  have  to  make  a  cir- 
cular groove  clear  around  the  tunnel,  across  the  floor,  roof 
and  walls  as  shown  in  Plate  XCIV;  the  fragments  from 
his  work  drop  into  the  candlebox  or  onto  the  muslin. 

According  to  the  length  of  the  workings  or  the  need  for 
great  accuracy,  he  repeats  this  operation  at  intervals  which 
may  be  every  5  feet,  10  feet  or  20  feet;  at  intervals  of  say 
20  feet,  he  masses  and  mixes  together  all  the  samples, 
breaks  them  up  as  fine  as  he  can  on  a  shovel  and  divides 


II  i 


'93 

the  result  into  four  parts,  throws  away  three  partu  and  re- 
tains one.  This  he  reduces  to  a  fine  powder  and  wrapH  up 
in  the  small  muslin  pieces,  ties  it  up  and  ttcalH  with  Heal- 
ing wax,  marking  on  it 
the  number  and  other 
notes,  such  as  lo  feet 
from  entrance,  etc., 
with  an  indelible  pen- 
cil. This  work  he  con- 
tinues till  he  has 
reached  the  end  of 
the  tunnel,  which  ii  it 
be  loo  feet  long  will 
give  him  from  20  feet 
intervals,  five  little 
sacks  of  powdered  ore 
for  assaying.  As  a 
check  upon  this  work 


Pl,AIK    XCl. 

Naiurnl  AppeMi'iinrx  itt  Mill*  un  «  BUnket 
()r«  DvpoMii, 


and  for  reference  in  caHe  of  any 
xccident'to  or  any  tampering  with  his  namplen  in  transit, 
e  will  occasionally  take  a  "  grab"  sample  from  hi»  broken 


Plate  XCII. 

Geological  Section  Showing  Workings  and  Off  HodiuH  lit  ('«intui't  HUnket 
Ore  Body.    Shaded  Hortionii  are  All  Worked  Out. 


rock  before  quartering  it.     Here  and  there,  too,  he  may 
take  a  chunk  of  some  peculiar  rock  such  as  a  porphyry  or 
some  peculiar  streak  in  the  gangue,  these  he  will  put  in  his 
coat  pocket  and  keep  on  his  person. 
It  is  sometimes  important  in  a  vein  to  find  (»ut  what  rock 

13 


194 

or  portion  of  rock  carries  the  most  value.  For  instance, 
on  one  occasion  we  examined  a  vein  said  to  carry  gold 
clear  across  its  entire  width  of  some  50  feet.  Now  this  so- 
called  vein  proved  to  be  a  decomposed  dyke  of  porphyry 
impregnated  with  pyrites  and  free  gold,  and  through  the 
dyke  ran  a  net-work  of  little  narrow  quartz  veins  or  veinlets. 
On  sampling,  whilst  we  took  samples  clear  across  the 
whole  width  of  the  vein,  we  kept  those  fragments  which 
came  from  the  quartz  veinlets  apart  from  those  which  came 
from  the  porphyry  gangue.  The  result  was,  we  found  the 
porphyry,  constituting  of  course  the  main  element,  to  be 
Darren  and  the  gold  to  be  concentrated  in  the  quartz  vein- 
lets  constituting  a  minimum  of  the  width. 
So  in  a  vein  there  will  generally  be  parts  richer  than 


i  I. 


ii 


Plate  XCIII. 

Piano-Section  of  a  Flat  Ore  Body. 

others,  "  pay  streaks"  as  they  are  called,  which  it  is  impor- 
tant to  distinguish,  also  certain  metallic  minerals  in  the 
vein  carrying  greater  values  than  others.  Thus  the  py- 
rites, if  undecomposed,  may  prove  too  poor  to  treat  for 
gold,  or  in  a  silver  mine,  streaks  of  gray  copper  may  be 
very  rich,  whilst  bodies  of  coarse  galena  may  be  very  poor. 
In  a  gold  mine  it  is  important  for  the  engineer,  if  he  can, 
to  find  out  to  what  depth  surface  decomposition  or  oxida- 
tion has  penetrated,  because  in  this  brown  rusty  matter 
will  likely  be  most  of  the  "  free  gold ;"  whilst  when  the 
unoxidized  pyrites  makes  its  appearance  the  ore  is  no 
longer  free  ore,  but  must  be  treated  by  some  process  other 


»95 

than  that  of  a  stamp  mill,  and  with  the  incoming  of  pyrite 
the  palmy  days  of  the  gold  mine  may  be  at  an  end.  Some- 
times, however,  though  the  oxidized  brown  gossan  may 
play  out  and  succeed  to  white 
quartz,  the  latter,  if  it  be  not  too 
hard,  white  and  "  hungry,"  may 
still  continue  to  carry  free  gold 
in  it.  Again  in  the  veins,  with 
their  descent  into  depths,  greater 
or  less  richness  may  occur  or 
different  varieties  of  ore  set  in. 
or  absolutely  barren  quartz,  so 
if  there  be  shafts  or  tunnels  driv- 
en on  the  vein  a  distinction 
should  be  noted  with  descent,  as  Plate  XCIV 

to  values  found  at  different  lev-        ^       ^^,.     ^      " 

els,     also     as     to    character   and  Expert  Taking  Samples. 

richness  of  the  ore  above  and  below  water  line ;  the  latter 
corresponds  to  the  average  drainage  level  of  the  country. 


il 


n 


Plate  XCV. 

Fissure  Vein  Outcrop  on  Hillside  Showing  Surface  Workings. 


This  completes  his  underground  examination.  Whilst  in 
the  mine  he  may  make  a  rough  sketch  or  two  of  the  vein 
showing  the  general  disposition  of  the  ore  bodies  or  any 
peculiarities.  On  emerging  and  carefully  .securing  his 
samples  beyond  reach  of  their  being  tampered  with,  he  se- 


^  196 

lects  a  convenient  point,  possibly  on  a  neighboring  hill 
facing  the  property,  and  takes  a  general  sketch  of  the  prop- 
erty in  pencil  or  water-colors  (see  Plates  LXXXIX,  XC,  XCI 
and  XCII),  also  makes  a  pencil  sketch  and  ideal  section  of 
the  hill,  showing  the  position  of  the  vein  and  its  workings 
(see  Plates  XCV  and  XCVI),  the  amount  of  ore  stoped  out 
and  the  amount  presumably  in  place  intact;  to  estimate 
the  latter  is  often  a  difficult  and  uncertain  problem.  He 
may  make  some  sort  of  estimate  as  to  the  reasonableness 


Plate  XCVI. 

Cross  Section  of  Vein  Showing  Workings.     Dotted  Portion  is  Ore  I'.ody, 

.Shaded  is  Ore  Worked  Out. 


or  not  of  the  price  asked  and  give  his  estimate;  he  can 
form,  however,  no  true  estimate  of  the  value  of  the  ore 
bodies  till  he  has  had  time  to  assay  his  samples,  for  these 
are  the  crucial  test  of  the  value  of  the  property. 

In  writing  up  his  report  at  his  leisure,  which  will  most 
likely  be  read  at  a  general  meeting  of  the  company,  he 
cannot  be  too  clear,  simple  and  explanatory  in  his  account 
and  its  details,  as  it  is  to  be  remembered  that  the  company 
is  likely  largely  to  be  composed  of  men  unacquainted  with 
mining  and  mining  terms;  he  must,  therefore,  not  take  it 
for  granted  that  they  know  what  "stopes,"  "adits"  and 
"gouge,"  etc.,  are,  but  explain  as  he  goes  along,  accom- 
panying his  remarks  with  rough  sketches  to  make  his 
meaning  clear  and  put  the  members  of  the  company  as 
much  on  the  ground  as  possible.  We  ourselves  have  found 
that  it  is  not  necessary  generally  to  make  elaborate  notes 


m  the  field  or  to  write  pages  of  reading  matter  then,  pro- 
vided we  make  many  sketches  and  on  them  put  down  items 
such  as  length  of  workings,  etc.,  etc.  The  sketch  is  gen- 
erally the  notes,  and  when  the  engineer  returns  home,  his 
sketches  will  recall  vividly  all  he  has  seen  and  from  these 
he  will  write  his  report.  Upon  certain  matters,  however, 
such  as  involve  numbers,  he  should  be  very  accurate  in 
writing  notes  and  not  trust  to  treacherous  memory  for  them. 


DESCRIPTION   OK   IM.ATES. 

In  Plate  LXXXIX  we  have  an  actual  example  of  a  rather 
inaccessible  property  in  the  San  Juan,  which  with  Plate 
XC  shows  the  kind  of  sketches  to  accompany  a  report.  In 
Plate  LXXXIX  with  its  section,  it  will  be  observed  how  very 
high  up  the  mining  holes  and  prospects  are  perched,  in  most 
cases  over  1,000  feet  above  the  valley,  and  again,  before 
the  ore  can  be  brought  over  to  the  mill,  a  ravine  of  a  hun- 
dred feet  deep  occupied  by  a  boiling  torrent  has  to  be 
crossed.  Some  of  the  properties  might  be  worked  perhaps 
by  a  suspension  tramway  thrown  across  the  gulch.  In  an- 
other case  a  trail  has  had  to  be  cut  in  long  zigzags  of  some 
miles  before  the  bottom  of  that  could  be  reached.  An- 
other disadvantageous  feature  in  this  property  is  the  num- 
ber of  scattered  veins,  none  of  them  very  rich  by  itself ; 
this  involves  a  separate  plant  or  workings  for  each.  One 
good  vein  would  be  better  than  all  these  put  together. 
There  is  fine  water  power  on  the  property  and  plenty  of 
timber. 

In  Plate  XC  there  is  one  fine  rich  gold  vein  easily  ac- 
cessible and  easily  worked ;  below  it  lies  a  natural  basin 
and  abundant  water  which  makes  it  an  admirable  location 
for  the  stamp  mill.  This  Plate  gives  an  idea  of  the  rough 
kind  of  a  sketch  the  expert  makes  on  the  ground,  which  he 
embellishes  and  elaborates  on  his  return. 

Plates  XCI,  XCII  and  XCIII  show : 

(XCI.)  The  surface  appearance  of  a  "flat"  or  contact 
blanket  on  the  side  of  a  hill,  such  as  Leadville. 

(XCII.)  Cross-section  showing  the  position  of  ore  bod- 
ies, the  portions  worked  out  and  portions  probably  left  in 
reserve,  also  the  workings  of  the  mine  and  the  geological 
section,  together  with  a  prominent  fault. 


198 

(XCIII.)  Is  a  somewhat  ideal  sketch  of  the  probable 
relations  of  a  flat  ore  body  if  the  surface  matter  were  re- 
moved, or  rather  if  it  were  opened  like  a  book. 

Plate  XCIV  shows  the  expert  taking  samples  in  a  tun- 
nel driven  in  the  vein ;  the  vein  in  this  instance,  being  a 
very  large  one,  occupies  the  whole  width  of  the  tunnel; 
this  is  not  generally  the  case,  the  vein  and  ore  body  are 
more  commonly  observed  about  the  middle  of  the  roof, 
/.<r.,  if  the  vein  is  small. 

Plate  XCV  shows  the  outside  appearance  of  a  fissure 
vein  with  three  tunnels  down  in  it,  and  Plate  XCVI  shows 
cross-section  and  profile  showing  the  tu  nel  and  the  ore 
bodies  so  far  discovered  in  the  quartz  gangue  and  how 
much  has  been  worked  out. 


CHAPTER   XIV. 


PROSPF.CTING    IN  VARIOUS  REGIONS. 


THE    GREAT     NORTHWESTERN     PROSPECTING     FIELD. 


; 


In  former  articles  we  have  dwelt  a  good  deal  on  pros- 
pecting in  Colorado  and  the  Rocky  Mountains,  considering 
that  region  as  typical  and  comprehensive,  and  that  if  a 
prospector  knew  experimentally  that  regfion  thoroughly,  he 
would  be  pretty  well  posted  "or  tackling  other  regions  of 
the  West. 

The  main  and  general  features  of  geology  and  of  ore  de- 
posits are  very  similar  throughout  the  gfreat  West;  the 
differences  rather  lie  in  exceptional  cases. 

Let  us  take  a  general  view  of  the  great  northwestern 
prospecting  field  as  a  whole  before  we  take  region  by  re- 
gion. The  features  that  most  strike  us  are  the  compara- 
tive little  settlement  of  those  vast  areas,  the  chance  of  their 
being  comparatively  new,  and  little  tried  and  certainly  not 
exhaustively  prospected  regions;  the  vast  areas  that  for 
Various  physical  reasons  have  not  been  prospected  at  all, 
and  in  some  cases  not  even  entered  by  white  men.     These 


h 


»99 

are  alluring  prospects  for  the  daring  young  prospector  who 
longs  to  enter  some  region  in  which  he  could  say : 

"  I  am  the  first  that  ever  burst 
Into  this  silent  land. ' ' 

We  do  not  like  going  over  old  well-beaten  tracks.  We 
do  not  like  to  meet  a  prospect  hole  every  few  hundred 
yards,  or  after  following  up  "  float"  and  other  signs,  at  last 
to  come  to  the  ledge  in  expectation  of  great  things  and  find 
Bill  Smith's  ubiquitous  stake  staring  us  in  the  face.  Much 
of  the  Northwest  is  a  kind  of  untracked  region.  From  the 
various  accounts  th  ,  reach  us  there  is  no  lack  of  gold  in 
th.se  northern  regions.     The  placer  deposits  are  excep- 


Plate  XCVII. 

Alaskan  Prospectors  Breaking  Camp  at  Foot  of  Chilkoot  Pass. 

tionally  rich  and  large,  as  we  might  expect  them  to  be  in 
such  tremendously  glaciated  areas ;  and  the  finds  remind 
one  of  the  halcyon  days  of  Q^rly  California.  But  there  are 
great  difficulties  to  be  overcome,  not  met  with  in  Colorado 
or  the  Rocky  Mountain  region  generally,  and  requiring 
great  hardship  and  lots  of  pluck.  There  are  mighty  gla- 
ciers to  be  encountered,  networks  of  gieat  and  little  rivers 
to  be  crossed,  a  very  peculiar  climate  to  deal  with,  plenty 
of  mosquitoes,  vast  and  almost  impenetrable  forests  to  be 


200 


traversed,  while  a  thick  underbrush  and  profuse  vegetation 
cover  up  larji[e  area  of  unknown  wealth.  So,  whilst  the 
proiipector  of  Colorado  and  Rocky  Mountain  experience 
may  have  found  his  pick  and  shovel  and  pan  all  that  was 
hitherto  necessary,  in  these  new  regions  he  must  add  to  his 
outfit  a  canoe,  a  pair  of  snowshoes  and  a  sleigh,  and  in 
place  of  the  "  burro,"  a  pack  of  native  sleigh-dogs,  and, 
above  all,  he  must  carry  a  good  axe,  or  even  a  long  cross- 
tut  saw,  as  often  he  will  have  literally  to  hew  and  saw  his 
way  to  fortune.  Said  a  prospector  just  arrived  from  those 
regions :  "  Prospecting  is  hard ;  the  country  is  heavily  tim- 
bered, with  much  underbrush  and  fallen  timber.  The  pros- 
pector has  to  pack  his  tools  on  his  back  and  cut  his  own 
trail  through  the  wilderness ;  when  he  finds  a  favorable 
location  he  makes  his  central  camp,  and  works  from  that. 
Game  is  not  plentiful.  In  the  veins  they  find  sometimes  a 
•  cap '  rock  rusty  with  oxidized  iron,  broken  over  and  cap- 
ping the  veins.  This  cap  is  two  to  four  feet  deep.  Then 
the  rock  passes  down  into  hard  unoxidized  pyrites.  Pros- 
pecting is  hard  and  slow,  for  you  have  to  blast  from  grass 
roots.  Caps  are  poor.  The  best  ore  is  found  with  depth. 
The  veins  in  this  region  have  not  been  much  prospected, 
attention  being  confined  mostly  to  placer  and  river  de- 
posits. Those  veins  I  saw  were  rich  and  narrow,  with  free 
milling  quartz  doubtless  down  to  a  limited  depth  below 
the  surface.  There  are  few,  if  any,  large  mines  between 
the  Selkirk  range  and  the  Rockies.  Veins  may  carry  both 
gold  and  silver,  but  principally  the  former,  and  that 
mostly  in  arsenical  pyrites.  Galena  and  silver  ores,  how- 
ever, occur  locally.  In  Idaho,  on  the  Snake  River,  placers 
are  worked  on  bars  at  the  surface  line  of  low  water.  The 
gold  is  fine,  light,  and  hard  to  save.  At  Spokane  the  river 
valley  consists  of  barren  wastes  of  sand.  The  sand  breaks 
farther  up  between  Idaho  and  Oregon.  Banks  are  low,  and 
long  bars  are  worked  which  are  washed  up  on  bends  and 
islands  right  down  to  the  water  line.  The  soil  is  alluvial 
in  this  part  with  no  glacial  matter.  Various  machines  are 
used,  and  pumping  plants  are  necessary,  as  there  is  no 
head  or  gravity  line.  In  British  Columbia  gold  can  be 
found  in  nearly  every  stream.  The  Columbia  River  is 
thirty-five  feet  between  high  and  low  water  mark  six 
months  of  the  year.     Placers  shift  and  change  with  every 


flood  season.  The  first  gold  worked  in  paying  quantities 
is  forty  miles  north  of  Revelstoke  on  small  streams  com- 
ing in  from  the  East.  Every  stream  running  from  the  east 
side  contains  placer  gold  as  far  north  as  (Voldstream,  sev- 
enty-five miles.  The  country  has  been  worked  and  pros- 
pected for  the  last  seven  or  eight  years.  The  altitude 
of  the  Columbia  is  2.000  feet  above  sea  level  and  the 
higher  ranges  about  8,000  feet.  Glaciers  extend  down 
to  a  level  of  4,000  feet,  and  are  still  working  and  grind- 
ing down  gold,    and  the   best  pay  has  been  found  late 


Plate  XCVIII. 

A  Glacial  Keffion  Showing  Living:  Glaciers  Leading  np  to  Amphitheatres 

and  U  .Shaped  Canyons. 

in  the  season  of  October  at  the  foot  of  the  glaciers. 
The  side  streams,  as  well  as  the  Columbia,  are  raging  tor- 
rents from  June  ist  to  September,  but  are  worked  about  a 
month  in  spring,  in  April,  and  in  the  fall  in  September  and 
October,  and  between  the  thawing  out  in  April  and  the 
floods  of  May.  In  the  fall  they  are  worked  in  September, 
after  the  floods  have  run  off  and  before  the  hard  freezing 
of  October.  This  high  water  is  caused  by  melting  snows, 
by  warm  weather.  Rain,  contrary  to  what  might  be  sup- 
posed, lowers  the  water  in  the  streams  because  it  makes 
the  water  so  cold  on  mountain  tops  that  it  checks  the  melt- 
ing of  snows,  and  the  highest  water  is  during  clear,  bright, 
hot  weather.     The  snow  rather  than  the  rain  is  the  cause 


203 


of  rlne  or  fall  of  the  rivers.  The  gold  is  fairly  coarse,  anc! 
found,  as  coiinnonly  elsewhere.mostly  at  bed-rock  and  near 
the  bed  or  channel  of  the  present  streams,  also  at  the  bot- 
tom of  boulder  and  glacial  debris  to  a  depth  of  20  to 
80  feet.  As  an  example  of  the  richest  of  these  placers, 
and  the  difficulty  of  getting  it,  as  well  as  the  enduring 
pluck  of  the  prospectors,  we  may  cite  that  of  the  Last 
Chance  placer.  The  prospectors  worked  four  years  in  an 
endeavor  to  dig  down  to  bedrock,  a  depth  of  only  60 
feet,  but  with  a  river  of  water  to  contend  with,  and  only  a 
few  months  in  the  spring  and  fall  available  for  working. 
They  were  drowned  out  in  summer  and  frozen  up  in  win- 
ter. The  prospectors  made  their  own  wooden  wheels  and 
pumps,  packed  everything  over  a  rough  trail  75  miles 
on  mules.  They  had  to  make  bridges  across  streams 
which  were  liable  to  be  washed  away  again  before  another 
trip.  For  supplies  they  would  make  two  or  three  trips  in 
the  summer  season.  The  first  season  they  drifted  on  bed- 
rock, hoisting  the  dirt  to  the  surface  and  washing  it  in  a 
common  sluice  box.  In  one  short  season  in  this  way  they 
took  out  $7,000,  the  following  year  $10,000,  and  the  next 
the  same.  On  some  of  the  streams  they  are  hydraulicking, 
with  an  old-fashioned  canvas  hose  with  brass  nozzle,  like 
a  fire-hose,  with  fifty  feet  head  of  water-power,  stripping 
the  surface  for  some  twenty  to  thirty  feet.  Some  are 
working  on  benches  not  in  well-defined  channels  and  with 
glacial  drift  full  of  immense  boulders  to  contend  with. 

"In  places  they  work  up  almost  under  the  present  gla- 
ciers. The  main  aim  is  to  get  down  to  bed-rock,  often  at 
considerable  depth,  getting  a  little  pay  gold  as  they  go 
down.  Prospectors  go  off  in  canoeing  parties  up  the 
rivers,  landing  here  and  there  and  prospecting  the  bars 
along  the  river  reaches.  The  first  glacier  I  met  with  was 
near  Revelstoke.  These  glaciers  are  narrow  necks  of  ice 
leading  up  to  big  basins  full  of  ice.  One  of  these  glaciers 
was  400  feet  deep  (Plate  XCVIII.). 

'  •  The  Kootenai  country  lies  east  of  the  Columbia,  between 
the  Canadian  Pacific  Railway  and  the  boundary  at  the  end 
of  the  Selkirk  range.  Galena  and  silver  ores  are  princi- 
pally found  north  of  Spokane  country.  The  region  is  steep 
and  rugged  like  parts  of  the  Colorado  Mountains.  It  is  a 
great  region  for  snow-slides,    another  peril  to  the  pros- 


903 


pector,  but  an  agency  by  .vhich  rich  veins  are  often  uncov- 
ered and  float  distributed.  These  snow-slides  cut  long 
swathes  through  the  thick  timber  and  pile  up  a  big  bnnk 
of  debris  in  the  valley  below.  Several  large  mines  are 
worked  in  this  district  rich  in  silver,  from  300  to  500 
ounces  to  the  ton.  There  is  a  smelter  at  Pilot  Hay,  on  the 
Kootenai  Lake,  and  another  at  Trail  Landing  on  the  west 
side  of  the  Columbia.  Ores  are  hard,  being  arsenical 
pyrites,  carrying  gold  and  silver,  one  to  three  ounces  gold 
and  10  per  cent,  copper  and  some  silver.  Bars  of  this  ore 
occur  in  the  granite,  and  the  ore  is  •  frozen  '  on  to  the  walls 
— that  is,  there  is  no  parting  selvage  or  gouge  between  the 
ore  and  the  country  rock.  The  War  ICagle  and  O.  K.  are 
shipping  between  them  200  tons  per  day,  principally  gold. 
The  average  is  two  ounces  of  gold  or  $50  per  ton.  Bound- 
ary Creek  as  well  as  Trail  Creek  report  y.*HK\  prospects.and 
the  mineral  belt  extends  south  into  Wasliington,  but  is  cov- 
ered at  present  by  Indian  reservations,  which  precludes 
prospecting. 

"  The  Fraser  and  Cariboo  districts  lie  west  of  this  region. 
There  are  some  expensive  hydraulic  plants  in  the  Quesnul 
and  Horsefly,  with  50  miles  of  ditch  on  each  plant;  several 
thousand  feet  of  steel  pipe  and  large  siphons  and  storied 
reservoirs,  preparing  for  next  season.  The  gravel  banks 
are  30  to  60  feet  deep  and  average  from  50  cents  to  $2  per 
cubic  yard,  so  it  is  said.  The  company  must  have  good 
assurance  of  the  great  richness  of  the  gravels  to  warrant  so 
expensive  an  outlay.  The  main  obstacle  outside  of  the 
shortness  of  the  season  is  from  immense  glacial  boulders. 
These,  in  all  placer  mining,  are  obstructions  owing  to  the 
difficulty  in  handling  them.  They  may  have  to  be  blasted 
or  lifted  out  by  derricks,  and  many  an  otherwise  rich  de- 
posit has  had  to  be  abandoned  owing  to  the  insurmountable 
difficulties  from  a  preponderance  of  these  boulders.  On 
the  Fraser,  Chinese  and  Indians  wash  bars  every  fall  and 
spring  at  low  water  with  rockers,  sluices,  etc.,  making  a 
living.  On  the  Middle  Fraser  dredges  are  at  work,  costing 
$75,000  per  dredge,  dredging  up  sand  and  gravel  fifty  feet 
below  the  water  surface.  In  Horsefly  country,  worked 
since  i860  successfully,  they  put  down  a  'wing  dam'  or 
caisson  to  bed-rock,  and  clean  up  well.  In  parts  of  Alaska 
they  work  the  gold  gravel  out  m  frozen  blocks  and  pound 


204 

it  up  in  the  spring,  and  work  '  drift  mining  '  in  this  way  alt 
the  winter.  The  gravel  beds  never  thaw  out  in  Alaska. 
Throughout  British  Columbia  transportation  is  by  horse, 
but  they  use  canoes  where  they  have  Kkes  or  can  go  down 
stream.  The  streams  are  too  swift  to  ascend  in  that  way. 
Leaving  the  travelled  trail,  you  have  to  carry  things  on 
your  back.  Trails  have  to  be  made,  and  prospectors  carry 
big  cross-cut  saws  as  part  of  their  outfit  and  saw  through 
the  timber  and  fallen  logs."  Such  is  my  friend,  Mr.  L.  T. 
Preston's,  comprehensive  account  of  prospecting  over  this 
region  from  his  own  personal  experience  of  several  months. 
Of  course  he  did  not  go  everywhere  and  see  everything, 
but  the  general  sketch  will  give  us  the  best  possible  idea 
of  what  is  before  the  prospector  in  the  great  Northwest, 
principally  in  Idaho,  Oregon,  Washington  and  British  Col- 
umbia.    Alaska  he  did  not  penetrate  far  into. 


PROSPECTING     IN   ALASKA. 

After  our  brief  sketch  of  some  of  the  leading  features 
from  a  prospector's  point  of  view  of  the  Northwestern  field, 
we  will  take  up  some  of  the  prominent  mining  and  pros- 
pecting areas  in  that  vast  region. 

Beginning  with  Alaska,  the  most  northerly,  the  least  ex- 
plored, the  most  attractive  and  unique.  A  glance  at  the 
map  shows  the  outline  of  its  coast  to  be  the  most  ragged 
on  the  globe.  The  coast  line  is  made  up  of  an  intricate 
network  of  islands  divided  from  one  another  by  a  laby- 
rinthine network  of  channels,  which  lead  you  so  far 
inland  that  it  is  doubtful  where  the  island  zone  and  the 
true  continent  begin  or  end.  These  labyrinthine  channels 
are  only  paralleled  in  their  intricacy  by  the  network  of 
great  and  little  rivers  which  seem  to  cover  the  surface  like 
the  ramification  of  ditches  in  a  quagmire  swamp.  It  is  a 
land,  too,  especially  near  the  coast,  of  great  mountain 
ranges,  which,  like  the  other  characteristics,  are  cut  up  ac/ 
infinitum  by  ravines  and  canyo.is ;  and  lying  in  the  depths 
of  those  canyons  is  the  migh.y  glacier,  the  key  to  all  this 
extraordinary  sculptured  and  tattered  and  river-traversed 
and  canyoned  aspect  of  the  region.  Alaska,  from  its  ex- 
treme northerly  position,  has  been  intensely  glaciated  both 
by  the  primeval  ice  sheet  of  the  glacial  epoch  and  by  sub- 


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190 

Plate  XCIX. 

M*t>  of  AlMka. 


f$$  tmuttnmmiii  t»immL* 


'n": 


i     ^K" 


205 

sequent  glaciers,  many  of  which  are  still  remaining  in  the 
mountain  fastnesses,  or  running  down  into  the  fiords  that 
open  into  the  sea.  These  are  still  doing  the  work  of  their 
predecessors,  viz.,  wearing  down  mounta'ns,  cutting  can- 
yons, exposing  veins,  grinding  down  gold-bearing  rocks, 
and  filling  up  ravines  and  valleys  and  river  bottoms  with 
placers  and  gold  bars.  Consequently  the  prospector  will 
expect  to  find  this  country  the  paradise  of  placers.  Bui, 
again,  the  mountains  being  a  continuation  of  the  Great 
Cordillera  system  have  the  same  crystalline  granite  core, 
the  mother  of  gold,  and  this  is  traversed  by  many  eruptive 
rocks,  porphyries,  and  old  lavas,  and  even  overflown  in 
places  by  modern  lavas  from  "  craters"  still  in  a  state  of 
active  eruption.  Here,  then,  are  elements  the  readers  of 
this  book  will  have  recognized  as  "  good  sign"  to  the  pros- 
pector for  finding  gold  veins  and  gold  and  silver  deposits, 
viz.,  granite,  eruptive  and  volcanic  rocks,  and  much  dis- 
turbance, heat  and  metamorphic  action.  Like  all  pioneers 
in  a  new  country,  the  prospector  will  most  likely  begin 
with  placer  mining,  and  end  up,  it  may  be,  by  the  discov- 
ery of  the  lead  or  vein  from  which  the  gold  came. 

Vast  areas  of  gold-bearing  territory  lie  partly  in  British 
Columbia  and  partly  in  Alaska,  known  as  the  Yukon  coun- 
try. In  1887  coarse  gold  was  found  on  tributaries  of  the 
Yukon.  At  low  water  these  tributary  streams  yieldeti 
large  profits,  from  $50  to  $100  per  day  by  sluicing.  The 
rich  spots  on  the  low  bars  were  worked  out  and  led  to  dis- 
coveries on  Forty  Mile,  Glacier,  Birch  Creek  and  others. 
High  bars  are  also  rich  and  untouched,  owing  to  the  diffi- 
culty of  getting  water  on  them  and  the  frozen  condition  of 
the  ground.  The  largest  nugget  found  was  valued  at  S42. 
SuHie  deposits  are  covered  by  twenty-five  feet  or  more  of 
loam  before  pay  gravel  is  reached.  Single  clean-ups  have 
been  made  of  55  pounds  of  gold  and  $36,000  in  gold  dust 
taken  out  in  a  season.  On  Glacier  Creek  pans  of  dirt  run 
from  a  few  cents  to  $4.  On  Bircli  Creek,  remarkable  for 
the  number  of  elephant  bones  found  in  its  gulches,  very 
rich  finds  have  been  made.  Prospectors  have  got  as  high 
as  $13  to  the  pan.  The  gold  is  described  as  like  pumpkin 
seed,  yielding  $3  to  $10,  and  sometimes  under  a  big  boulder 
or  a  little  stone  on  bed-rock  they  could  pick  up  from  $15 
to  $20. 


2o6 


SILVKR    HOW    HASIN. 


The  first  important  discovery  of  gold  in  Alaska  was  in 
Silver  Bow  Basin  in  1880  in  gravels  of  Gold  Creek.  The 
discovery  and  progress  of  this  district  is  very  instructiv 
to  the  prospector.  The  first  prospectors  came  on  the  de- 
l)<)sits  on  the  hillside,  and  soon,  as  they  supposed,  cleaned 
fiut  everything  in  the  Basin.  But  a  Mr.  Nowell,  quietly 
looking  over  things,  decided  to  tap  the  bottom  of  the  basin 


Plate  C. 

Silvir  How  Basin  Looking  Soutlit'ast,  Showing  Placer  and  otlivr  Mining 

Operations. 

with  a  tunnel  to  be  used  as  a  sluiceway  and  so  work  the 
entire  basin  on  a  large  and  systematic  scale.  The  first 
prospectors  on  the  hillsides  exposed  numerous  quartz 
veins,  and  stringers  of  quartz  under  the  placers  in  bed-rock. 
They  located  a  few  holes  on  these  veins,  but  having  noth- 
ing but  an  arastra  to  work  with,  soon  abandoned  the  vein 
mining.  Several  patterns  of  mills  were  tried  on  the  flint- 
like quartz  unsuccessfully,  till  a  Webster  mill  with  five 
stamps  and  later  ten  stamps  proved  a  success.     The  veins 


!! 


207 

are  called  "  contact  vein  fissures,"  the  reef  having  a  black 
slate  hanging-wall  and  a  greenish  gneiss  foot-wall.  Be- 
tween the  walls  of  contact  a  space  of  several  hundred  feet 
occurs,  filled  in  with  schists,  quartz  veins,  and  vein  matter. 
The  filling  is  networked  with  veins  from  a  knife  blade  to 
several  feet  in  thickness,  according  to  the  Alaska  Record, 
which  also  says:  "  The  ore  in  Silver  Row  Basin  is  iron  py- 
rites and  galena  with  zinc  blende,  antimony,  copper  pyrite, 
carrying  gold  and  silver,  but  richer  in  gold,  in  some  veins 
in  this  basin  now  silver  and  now  gold  predominates.  Mill- 
ing consist  in  reducing  their  bulk  by  concentration  without 
free  gold-saving  appliances.  Where  the  gold  reef  leaves 
the  valley  and  climbs  the  mountain  sides,  veins  outcrop  on 
the  surface.  So  there  was  not  much  difficulty  in  tracing 
the  reef  through  Silver  Bow  Basin  to  the  summit  of  the 
divide,  where  veins  were  found  cropping  just  beyond  the 
upper  break  of  the  glacier.  Some  of  these  croppings 
showed  upwards  of  48.6  ounces  of  gold  to  the  ton.  The 
Gold  and  Curry  mine  lies  north  of  the  reef  and  is  a  chim- 
ney or  up-shoot  from  the  main  mineral  zone.  It  shows  on 
the  surface  for  several  hundred  f'set  a  number  of  well-de- 
fined perpendicular  veins  running  high  in  gold.  Great 
granite  dykes  cut  through  the  slates  east  of  Takon  Inlet, 
and  run  for  a  long  distance  down  the  coast  from  north  to 
south,  belonging  to  the  same  general  zone  of  mineralized 
disturbance." 

Sum  Dum  Bay,  Shuck  Bay  and  Basin  Reef  have  all  their 
noted  ore  deposits,  and  along  the  mainland  and  numerous 
islands  indications  of  mineral-bearing  bodies  exist  in  veins 
of  quartz  with  "  colors"  in  the  streams,  while  in  the  lime- 
stone of  Glacier  Bay  rich  silver  ores  occur.  In  Admiralty 
Island  the  Willoughby  group  of  veins  cut  diagonally  across 
a  gneissic  formation.  The  veins  are  from  a  foot  to  ten  feet 
wide  and  entirely  gold-bearing. 

BEACH    SANDS. 


Rub)''  and  black  sand  arc  found  along  the  beach  at  the 
foot  of  the  Fairweather  range  for  many  miles  up  the  coast. 
They  are  rich  in  fine  gold,  but  heavy  and  bright,  amalga- 
mating readily  and  by  sluicing.  The  deposits  come  from 
grinding  glacial  action  in  the  ranges  back  of  them,  streams 


2o8  •    \ 

carry  the  sand  to  the  sea,  and  the  surf  rocks  and  pans  and 
separates  the  heavy  material,  leaving  it  in  alternate  layers 
and  windrows  along  the  beach.  The  black  and  ruby  sand 
and  gold,  being  the  heaviest  inaterials,  naturally  affiliate. 


1 


COPPER    RIVER. 

The  Copper  River  section  is  one  of  romantic  interest 
and  speculation.  Natives  living  at  the  headwaters  used 
copper  implements  and  brought  down  to  the  coast  chunks 
of  native  copper  to  the  Russians,  who  were  thus  tempted 
to  explore  the  source,  but  ill-treating  the  natives  after  their 
wont,  the  exploring  party  were  brained  when  asleep. 
Prospectors,  since,  who  have  tried  to  ascend,  have  been 
intimidated  by  glaciers,  swift  currents  and  rapids,  high 
precipitous  banks  and  other  almost  insurmountable  diffi- 
culties. So  the  upper  Copper  River  is  still  an  unsolved 
problem. 

At  the  head  of  Cook's  Inlet  Russians  placer-mined  for 
years.  Rich  diggings  and  much  coarse  gold  were  found 
lately  at  Turn-again  Arm.  Both  silver  and  gold  are  mined 
in  Unja  and  Unimak  Islands,  the  ore  running  from  $24  to 
$143  to  the  ton.  A  stamp  mill  here  high  above  the  mouth 
of  the  Yukon  is  the  most  northern  mill  in  the  world. 


DISCOVERY    OK   THE   TREADWELL    MINE. 

The  discovery  of  the  Treadwell,  the  most  noted  mine  in 
Alaska,  as  told  in  the  Alaska  Mining  Record,  is  another  in- 
structive lesson  to  the  prospector. 

Like  many  other  instances,  the  discovery  of  gold  in 
placers  led  to  the  discovery  of  the  renowned  Paris  or 
Treadwell  mine. 

On  the  27th  of  January,  1882,  prospectors  from  Juneau 
crossed  Gastineaux  Channel  to  Douglas  Island  and  found 
pay  dirt  upon  the  beach,  and  the  following  March  they 
washed  on  ground  called  Ready  Bullion,  and  in  three  days 
washed  and  cleaned  up  27  ounces  of  gold-dust.  This  led  to 
finding  another  deposit  of  gold  dirt  and  decomposed  quartz, 
and  in  washing  the  gravel  from  the  bedrock,  the  great  Tread- 
well ledge  ivas  exposed.  Peter  Erussard,  or  "  French  Pete," 
located  the  ledge,  calling  it  the  "  Paris."  Placer  miners, 
however,  by  right  or  might,  held  the  surface  for  two  years 


209 


and  washed  out  amounts  estimated  at  $50,000  to  §100,000. 
Nothing  was  done  by  "  Pete,"  as  he  considered  the  ore  t<Mi 
low  grade  to  work  profitably.  Then  came  along  one  of 
those  characters  so  often  figuring  in  the  history  of  great 
mines,  a  far-seeing  man,  named  John  Treadwell,  who  made 
a  thorough  examination  of  the  ledge,  its  facilities  for  work- 
ing and  opening  up,  as  well  as  the  character  of  the  ore  by 
assaying,  and  opened  negotiations  for  purchase.  French 
Pete  was  glad  to  let  "  the  worthless  thing"  go  for  $400. 
Treadwell  organized  the  Alaska  Mill  and  Mining  Company, 
and  began  driving  a  cross-cut  prospecting  tunnel  toward 
the  veins,  and  erected rt  five-stamp  mill  (not  a  hundred-stamp 
mill  as  is  often  so  foolishly  done  at  the  outset)  to  test  by 
mill-run  the  true  value  of  the  ores  before  he  went  further 
and  while  the  tunnel  was  being  driven  in  toward  the  ledge. 
When  the  cross-cut  reached  the  opposite  wall  it  showed  up, 
instead  of  the  obscure  veins  on  the  surface,  a  ledge  of  four 
hundred  feet  width  of  nearly  solid  quartz !  And  the  little 
stamp  mill  proved  that  the  average  value  of  the  ore  was 
sufficient  to  make  the  mine  pay  if  worked  on  a  /urge  sys- 
tematic scale.  In  1883  a  120-stamp  mill  was  erected,  and  in 
1890  added  chlorination  and  doubled  the  capacity  to  240 
stamps.  More  claims  were  purchased,  and  wharfs  and  rail- 
way tracks  and  the  largest  works  in  the  world  soon  showed 
that  this  mine,  from  the  little  beginnings  of  the  prospector, 
had  assumed  the  rank  of  one  of  the  foremost  in  the  world. 
The  power  that  drives  the  great  machinery  is  an  18-mile 
ditch,  extending  along  the  mountain-side,  applied  to  a  Pel- 
ton  water-wheel  under  a  520-feet  pressure,  with  Corliss  en- 
gines also  added.  The  240  stamps  weigh  each  850  pounds, 
with  96  drops  per  minute.  The  mill  has  a  capacity  of  700 
tons  of  ore  per  day  and  chlorination  of  18  tons  of  pyrite 
daily.  The  average  grade  of  ore  is  only  $2.75,  carrying  2 
per  cent,  sulphurets ;  and  the  expenses  of  reduction  are  at 
the  extraordinary  low  figure  of  $1.35.  Formerly  the  ore 
was  quarried  out  in  great  pits,  dropped  down  ore  shutes 
into  cars,  and  conveyed  through  a  tunnel  by  steam  and 
dumped  into  bins,  thence  into  crushers  and  batteries ;  but 
with  deeper  working  a  shaft  was  sunk  250  feet  below  the 
tunnel,  and  immense  hoisting  works  put  in  to  raise  the  ore 
to  this  level.  Two  hundred  men  are  employed  daily  at  $3 
to  $7. 

14 


lO 


I 


Mr.  H.  P.  Gushing,  speaking  of  the  Trcudwcll  mine  vein, 
says:  "The  gangue  is  for  the  most  part  white  transparent 
quartz,  which  has  been  considerably  crushed  and  thereby 
rendered  granular  and  opaque.  A  peculiar  greenish  rock 
is  also  found,  poorer  in  gold  than  the  quartz.  Pyrite  is 
evenly,  but  sparingly,  distributed  in  small  crystals.  Occa- 
sional streaks  of  quartz  free  from  pyrite  occur,  and  at  times 
pyrite  alone  constitutes  the  mass.  Horses  of  slate  were  oc- 
casionally met  with,  which  were  taken  out  with  the  ore 
and  sent  through  the  mill.  The  quartz  carries  a  certain 
amount  of  free  gold,  but  the  main  portion  is  enclosed  by 
pyrite  and  cannot  be  amalgamated.  Streaks  of  molybde- 
nite (like  graphite)  occur,  running  high  in  gold.  The 
Treadwell  is  an  example  of  an  ore  body  in  which  the  con- 
tent of  the  precious  metals  is  lo-.v,  yet  the  i)roperty  a 
good  paying  one  on  account  of  the  vastness  of  the  deposit 
and  the  ease  and  cheapness  with  which  it  is  worked.  It  is 
close  to  water  and  steamships,  plenty  of  mountain  water- 
power  and  abundance  of  fuel  and  timber.  Six  hundred 
tons  are  pulverized  daily  by  240  stamps  in  the  enormous 
stamp  mill.  The  outcrop  of  the  vein  stood  up  to  the  pros- 
pector's gaze,  owing  to  its  hardness  relatively  to  the  en- 
closing slates,  as  a  considerable  peak,  and  the  first  mining 
done  was  simply  the  working  off  of  this  peak.  Later  a 
tunnel  was  run  into  the  mountain  side,  cutting  the  vein, 
from       ich  the  ore  is  dumped  into  cars  below." 


CHAPTER   XV 


GEOI-OGV    AND    MINKRALOCY   OF   ALASKA. 


From  what  we  can  gather  from  Mr.  Gushing  and  the 
Alaska  Record,  the  following  appears  to  be  the  general 
geological  features  of  this  region : 

Along  the  headwaters  of  the  Yukon  are  high  ranges 
with  lofty  snow-capped  peaks  and  many  chains  of  lakes. 
In  the  gravel  along  the  sources  of  the  streams  gold  is  found 
and  bars  have  paid  fair  wages.  In  the  ranges,  veins  of  sil- 
ver, copper  and  lead  exist,  but,  their  location  being  some- 
what inaccessible  and  remote  from  any  ore  market,  are 


3f  I 


passed  over  by  the  prospector,  who  seeks  for  pluccr  ilig- 
jjinj;  only.  Bed-rock  is  mostly  granite,  together  with  some 
ancient  limestones  and  crystalline  slates  and  schists.  Ser- 
l)entine  also  appears  (usually  a  green  or  purple-streaked 
rock),  showing  a  continuation  to  the  north  of  the  cele- 
brated serpentine  schist  and  slate  belt  of  California  and  the 
Kootenay.  Caribou  and  Cassiar  districts.  Some  ranges  are 
like  the  highly  colored  mineral  belt  of  Red  Mountain  in 
Colorado.  Placer  mining  on  the  Yukon  is  still  in  infancy. 
According  to  Mr.  H.  P.  Cashing r  "The  geological  struc- 
ture of  this  region  is  very  complicated,  due  to  the  disturb- 
ances which  have  taken  place.  There  have  been  two  or 
more  different  periods  of  crust  movements.  The  original 
slialesand  limestones  have  been  shattered,  fissured,  faulted 
and  metamorphosed,  and  at  certainly  two  different  periods 
outflows  of  eruptive  rock  have  taken  place.  Great  numbers 
of  these  fissures  have  been  filled  with  metalliferous  matter. 
Small  veins  abound,  carrying  gold-bearing  pyrites,  gener- 
ally in  a  quartz  gangue  or  silver-bearing  galena,  and  sil- 
ver sulphurets  in  a  calcitc  gangue.  These  veins  are  found 
both  in  metamorphic  slates  and  limestones  and  in  eruptive 
rocks.  In  the  large  majority  of  cases  the  deposits  are  of 
no  value,  due  to  their  small  size  and  prevalent  leanness  of 
ore.  When  they  hold  out  promise  for  the  future,  it  is 
more  often  from  the  size  of  the  deposit  than  from  its  rich- 
ness." 

VEGETATION    OBSTACLES   TO    PROSPECTING. 

"  Owing  to  heavy  precipitation  and  hot  summers,"  says 
the  Record,  "  the  region  is  covered  by  a  dense  mantle  of 
vegetation  of  almost  tropical  luxuriance,  and  forests  cover 
the  land  from  water's  edge  to  timber-line,  save  where  cliffs 
are  too  steep  for  a  seed  to  lodge,  or  a  glacier  fills  a  ravine. 

"  No  forest  fires  have  devastated  these  shores.  The  scars 
of  winter  avalanches  are  quickly  covered  with  a  mantle  of 
living  green.  For  the  first  1,000  feet  above  sea  level  the 
forests  are  choked  with  densest  undergrowth.  A  jungle  of 
bushes  covers  the  mossy  pitfalls  of  decaying  logs  beneath. 
Above  that  zone  is  a  belt  where  ferns  and  mosses  riot,  and 
trees  spring  up  slender  and  straight  as  columns  in  a  vast 
cathedral,  where  there  is  ever  a  sombre  green  light  and 
dew  and  damp  moisture  left  by  tangled  clouds. 


21 


"  The  foot  sinks  in  a  thick  carpet  of  nio.sA.  and  one  treads 
with  muHled  steps  in  deference  to  the  sombre  silence  and 
solitude  that  reign  in  an  Ahiskun  forest." 

"  At  altitudes  of  2.000  feet  above  the  sea  there  nre  the 
wildest  fantasies  in  trees — wind*swept,  gnarled  and  crouch- 
ing  hemlocks,  borne  down  by  the  weight  of  winter  snows 
(like  the  stunted  spruce  at  tnnber-line  in  Colorado)  until 
what  should  be  a  lofty  tree  spreads  out  flat  like  a  mat,  the 
stump  growing  only  u  few  feet  high,  its  limbs  elbowing 
out  in  all  directions  and  the  whole  tree  covering  several 
square  yards  of  ground.  In  places  these  dwarfed  forests 
cover  the  surface  of  the  country,  and  the  traveler  has  at 
times  to  crawl  and  wind  his  way  by  lying  flat  on  his  belly 
under  the  low-spreading  branches,  or  clambering  up 
through  an  opening  flnds  a  sudden  seat  astride  a  limb  or 
in  some  other  awkward  position  among  the  boughs  in  this 
novel  mode  of  traveling  over  the  top  of  these  singular 
Alaskan  forests." 

A  picture  of  every-day  life  of  the  pioneer  prospectors  is 
thus  drawn  by  the  Jicconl: 

"  Imagine  a  group  of  bearded,  roughly  clad  men  squatted 
under  a  brush  spruce  or  hemlock  around  a  cracker 
box,  with  a  pot  of  steaming  mussels  between  them,  with 
French  Pete's  Si  wash  sugar  and  blackstrap  molasses  as 
dessert ,  and  later  in  the  evening  gathered  around  a  roar- 
ing log  fire  discussing  the  results  of  the  day's  'run'  in  the 
diggings  or  spinning  yarns  of  the  huge  nuggets  they  had 
taken  in  the  Caribou  district,  or  of  the  extreme  cold  in  the 
Cassiar  region.  A  devil-may-care  life  was  led  oy  the  pio- 
neers with  many  a  hardship,  yet  through  it  all  they  thrived, 
growing  strong  and  enjoying  the  hard  «  \ocks  incident  to 
a  prospector's  life.  Nor  were  these  hardships  and  dangers 
confined  to  land  in  this  semi-aquatic  country.  In  trying  to 
reach  the  coast,  parties  were  blown  ashore  and  their  canoes 
wrecked.  The  sole  resources  of  many  of  these  men  con- 
-sisted  of  a  sack  of  flour,  a  side  of  bacon,  a  few  pounds  of 
beans,  a  pick  and  .shovel,  and  a  canoe.  But  they  were  not 
discouraged,  for  they  knew  that  gold  lay  in  the  basin  above 
them ,  and  they  set  to  work  cutting  down  the  monarchs  ot 
the  forest  and  building  cabins  for  their  shelter  during  the 
long  months  of  approaching  winter." 


»M 


CHAPTER   XVI. 


HRITISH    AMKKICA. 

The  most  reliable  account  we  have  of  this  ^reat  region 
is  from  the  Canadian  xeolojjfist.  Mr.  O.  M,  Dawsnn,  and  in 
it  we  shall  see  much  that  will  refnind  us  of  Alaska  and  of 
other  regions  of  the  Northwest  as  well  as  those  bordiTing 
on  the  Pacific  coast.  There  is  a  family  likeness  between 
all  these,  owing  to  the  comparative  similarity  of  their 
geology.  British  America,  like  Alaska,  is  traversed  by  thi' 
same  Cordillera  system  of  uKmntains,  and  in  the  second 
place  has  been  glaciated  like  Alaska.  Hence  it  is  a  region 
of  fissure  veins  and  of  placers.  There  is  scarcely  a  stream 
in  British  Columbia  that  will  not  show  "colors."  The  va- 
riability of  the  product  depends  on  the  season;  the  great 
winter  snowfall  or  heavy  rainfall  retards  work  in  clearing- 
deep  claims  from  water  till  late  in  the  spring. 

The  general  distribution  of  alluvial  gold  indicates  that 
several  rock  formations  produced  it  in  greater  or  less  quan- 
tity, though  it  is  only  where  course  gold  occurs  that  the 
original  gold  veins  may  be  supposed  to  exist  in  the  imme- 
diate vicinity  of  the  deposits. 

Colors  travel  far  on  beds  of  rapid  rivers  before  they  are 
reduced  to  invisible  shreds.  Glacial  drift  also  distributed 
the  gold  widely.  The  formations  are  talcose  and  chloritic 
(i.e.,  greenish),  or  blackish  gray  slates  and  schists  much  al- 
tered by  heat,  they  appear  to  he  the  prolongation  north  of 
the  richest  gold-bearing  rocks  of  California.  Denudation 
of  these  veins  concentrated  the  gold  in  placers. 

The  noted  Caribou  district  is  a  high  plateau  cut  by  V- 
shaped  canyons,  whose  lessening  slope  is  concealed  by 
gravels  which  increase  in  thickness  till  the  valley  becomes 
U-shaped  or  flat-bottomed,  through  which  streams  flow  tor- 
tuously and  gently.  The  banks  are  densely  clothed  with 
firs  and  the  country  covered  with  drift. 

Shallow  placers,  as  usual,  first  attracted  attention,  and. 
later,  deep  diggings  in  due  order  were  attacked  and  foimd 
most  profitable.  Williams  and  Lightning  Creeks  yielded 
the  .crreater  part  of  the  gold  of  Caribou,  being  well   suited 


214 

for  dee^  work,  having  a  hard  deposit  of  boulder  clay  be- 
neath the  beds  of  the  present  water-courses  which  prevents 
the  access  of  much  of  the  superficial  water  to  the  workings 
below.  The  rocky  bottom  or  the  valley  is  followed  beneath 
50  to  150  feet  of  overlying  clays  and  gravels,  the  course  of 


.: 


'H 


'<-.'       \     /^    ^  S  H  I  N  G  T  0  N    \\        )        "'^--ih^ 


Plate  CI. 

I'ritish  C<)linnl)iii  Uokl  I'ielils.    (After  Locke.) 

the  ancient  stream  being  traceable  by  the  polished  rocks  of 
its  bed  and  coarse  gravel  and  boulders  filling  its  channel. 
The  richest  lead  of  gold  is  found  in  the  hollow  of  the  r- cky 
channel,  but  following  the  rock  surface  laterally,  side 
ground  rich  enough  to  pay  well  is  found  for  a  greater  or 
less  width.     Old  stream   courses  of   Caribou  jmrsuc   the 


'I 


I   I 


2'5 


same  direction  as  the  modem  rivers,  crossing  often  from 
side  to  side  of  the  valley  \vith  different  flexures,  but  never 
leaving  the  line  of  the  old  and  modern  valley  or  crossing  it 
as  in  California.  We  may  take  the  Van  Winkle  mine  as  a 
type.  On  reaching  the  buried  channel  a  shaft  is  sunk  on 
the  down-stream  end  of  the  claim  in  the  sloping  side  of  the 
valley  to  bed-rock  slate.  The  shaft  is  continued  to  a  cer- 
tain depth  in  this,  and  then  a  drift  is  started  at  right  angles 
to  the  course  of  the  valley.  The  right  depth  is  estimated 
by  that  found  in  other  workings.  The  old  channel  is  struck 
in  such  a  way  as  to  enable  the  subterranean  water  collect- 
ing in  it  from  the  whole  upper  part  of  the  claim  to  be 
jjumped  to  tlie  surface  by  the  shaft.  The  old  channel,  once 
reached  and  cleared  of  water,  is  followed  up  its  slope  by  the 
workings  to  the  upper  part  of  the  claim,  and  where  paying 
side  ground  occurs  it  is  also  opened.  The  richest  pay  is  ob- 
tained in  the  rock  channel  of  the  old  stream,  but  where  this 
is  much  contracted  the  force  of  the  water  has  swept  the 
gold  away  to  those  places  where  its  width  is  increased. 
The  hard  rocks  retain  their  polished  water-worn  forms,  but 
the  slates  are  rotten  to  a  considerable  depth,  and  on  cleaning 
up  on  the  bottom  a  thickness  of  one  to  two  feet  is  taken 
out  with  a  pick  and  shovel  and  sent  up  to  the  surface  with 
overlying  gravel  for  treatment.* 

In  the  central  channel  most  gold  lies  directly  on  bed-rock 
and  only  occasionally  in  pay  streaks  or  gravel  above  it  for  a 
few  feet. 

The  side  ground  is  worked  up  from  the  channel  in  suc- 
cessive breasts  parallel  to  it.  The  lowest  layers  of  gravel 
contain  many  boulders  of  quartz  and  slaty  fragments  fallen 
from  the  hillsides.  Water  is  the  main  difficulty  met  with, 
the  workings  being  annually  filled  by  spring  floods.  In 
working  over  the  deep  ground  in  early  days  in  the  Cariboo 
district  much  was  left  that  would  even  now  pay  handsomely, 
but  cannot  now  be  found  on  account  of  the  treacherous 
nature  of  the  moved  gravel  (a  lesson,  first,  that  old  care- 
lessly worked  placers  may  pay  to  work  over  again ;  secondly, 

■*  Rotten  rocks,  especially  slates  or  schists  below  placer  gravel, 
are  favorite  repositories  for  K<*lfl  '"  placer  mining,  and  the  pros- 
pector should  never  stop  his  search  till  he  has  dug  down  well 
into  this  rotten  bed-rock. 


3  I  6 

the  tlifficulty  of  working  old  Rroimd,  new  firm  ground  being 
far  easier ;  and  lastly  for  prospectors  to  work  a  placer  scien- 
tifically and  exhaustively  before  they  abandon  it). 

In  this  as  in  most  other  gold-bearing  countries  the  placers 
have  led  later  to  the  discovery  of  veins.  Several  of  these 
veins  have  been  traced  for  miles.  The  gold  occurs  asso- 
ciated with  iron  pyrites  and  galena,  through  crystalline 
masses  of  which  the  gold  is  sometimes  strung. 


i  Jl 


KOOTKNAY    DISTRICT. 

This  district  is  rugged  and  mountainous,  comprising  the 
soutli  portion  of  the  Selkirk  range  and  the  Columbia  or  gold 
range.  Between  these  ranges  are  a  string  of  lakes.  The 
ranjic'S  are  not  very  continuous.  The  rocks  are  mainly 
massive  granite,  in  places  overlain  by  stratified  rocks.  The 
ranges  average  8,000  feet  above  sea  level.  The  country  is 
densely  wooded.  Two  long,  deep  valleys  traverse  the  dis- 
trict norih  and  south,  one  occupied  by  the  Columbia  River 
and  Arrow  Lake,  the  other  by  the  Kootenay  lakes.  The 
lake  discharges  into  the  Columbia. 

(IKOI.OdV. 

The  oldest  stratified  rocks  are  mica  schists  and  gneisses 
and  some  crystalline  marbles  and  quartzites  of  Archaean 
age.  Overlying  these  at  Hot  Springs  are  gray  and  green 
schists  imconformable  and  newer  than  the  Archaean.  Over 
these  are  massive  gray  limestones  changed  locally  into 
white  marble  with  conglomerate  below.  The  green  schists 
are  composed  of  volcanic  detritus  made  schistose  or  slaty 
by  pressure.     The  thickness  of  the  series  is  32,000  feet. 

West  Kootenay  is  of  massive  granite  with  many  eruptive 
dykes.  The  granites  are  of  intrusive  eruptive  origin,  and 
later  than  the  stratified  rock  which  they  have  altered  by 
their  heat  at  the  contact.  They  are  closely  connected  with 
metalliferous  veins  or  stratified  rocks  deposited  at  the  time 
of  their  intrusion.  These  new  eruptive  granite  dykes  of 
a  reddish  color  cut  the  older  gray  granites  (as  at  Cripple 
Creek,  Colorado).  Most  of  the  mines  are  in  the  stratified 
rocks.  A  few  veins  traverse  a  hard,  dark-gray  mica  syenite 
(a  rock  not  imlike  gfranite),  and  are  gold-bearing  associated* 


!! 


<•  ( 


I  \ 


->» 


■  •**■■ 


217 

with  iron  pyrites  in  (jtiartz.  Those  in  stratified  rocks  carry 
i;alena,  blende  and  pyrite,  and  are  l<>\v  jj;rade  in  silver. 
Such  are  the  Hendryx  and  Hot  Springs  mines.  The  richer 
ores  at  Hot  Springs  are  in  green  and  gray  schists  and  lime- 
stones. The  richness  is  due  to  the  influence  of  country 
rock  and  proximity  to  the  granite.  Stratified  rocks  con- 
taining the  ore  deposits  of  Toad  Mountain  are  surrounded 
by  granite.  Alteration  of  rocks  is  due  to  the  heat  of  the 
granite.  So  the  country  rock  consists  of  altered  old  vol- 
canic material  derived  from  the  detritus  of  an  eruptive 
porphyry.  Greenish-gray  rocks  spotted  over  with  coarse 
porphyritic  white  crystals  of  plagioclase  feldspar  and  black 
augite  crystals  are  characteristic  of  the  ore-bearing  zone. 

The  Spokane  Mine  occurs  near  a  wide  belt  of  quartz  and 
a  dyke  of  eruptive  andesite  lava.  In  the  "  Number  One" 
the  rock  is  limestone  with  veins  cutting  across  it  north  and 
south  and  veins  traceable  for  miles.  Ores  range  from  20 
to  300  ounces  in  silver.  The  richest  deposits  are  in  lime- 
stones and  black  clay  slates.  The  ore  is  principally  silver- 
bearing  galena  decomposed  in  the  limestones  to  carbonates 
for  some  depth,  together  with  native  silver  and  gray  copper 
occurring  in  irregular  pockets  and  impregnating  the  lime- 
stone by  substitution,  as  at  Leadville,  Colorado. 

The  Cassiar  mines  are  worked  at  great  disadvantage  in 
an  Arctic  climate  with  the  soil  permanently  frozen,  with  a 
short  season  of  floods  disastrous  to  mines. 


THE  PECULIAR   GOl.D-BEARINd   ROCKS. 

On  Leech  River  are  some  persistent  gold-bearing  rocks 
found  through  British  Columbia,  showing  a  great  area  and 
extent  of  these  peculiar  rocks.  In  the  southern  part  of 
British  Columbia  these  rocks  are  black  slates  and  schists 
traversed  by  quartz  veins.  It  is  from  these  mainly  that 
the  placers  derive  both  their  material  and  gold.  In  pros- 
pecting the  extent  and  distribution  of  these  slaty  areas  is 
important,  though  only  a  portion  of  the  streams  flowing 
over  them  carry  gold  in  paying  quantities.  Still,  when 
once  the  prospector  has  become  familiar  with  these  rocks 
he  keeps  to  them  and  avoids  other  and  barren  regions. 

The  slates  are  sometimes  calcareous,  micaceous  and 
graphitic.     Probably  a  small  quantity  of  organic  matter  in 


2l8 


the  sediments  from  which  these  rocks  were  made  may  have 
aided  in  precipitating  metalliferous  matter  and  accounts  in 
part  for  their  richness.  Their  fissile  character  later  ren- 
dered them  easily  permeable  by  waters  which  have  con- 
centrated the  minerals  of  economic  value  with  quartz  and 
other  crystalline  minerals  of  secondary  origin  in  the  veins. 
Geologically  this  set  of  strata  appears  to  lie  between  the 
Carboniferous  and  Mesozoic  rocks  and  may  be  meta- 
morphosed Triassic  or  Jurassic  strata.  The  group  runs  all 
along  the  west  coast  from  California  to  Alaska,  and  a 
knowledge  and  recognition  of  them  as  the  gold-bearing 
series  is  of  great  importance  to  the  prospector.  The  rapid 
character  of  the  Eraser  River  has  distributed  the  finer 
particles  of  gold  throughout  its  entire  course,  though  the 
heaviest,  coarsest  gold  is  found  in  that  part  of  the  river 
occupied  by  the  slates.  Where  the  slates  are  absent  it  is 
derived  from  the  igneous  Tertiary  rocks,  volcanic  tuffs, 
breccias,  and  lavas,  which  often  yield  gold  placer  matter 
just  as  certain  volcanic  andesites  and  breccias  carry  gold 
in  Colorado,  and  are  worthy  everywhere  of  er^amination. 
Fine  gold  also  was  carried  far  by  the  ice  and  currents  of 
the  glacial  period.  On  the  Tranquille  River  the  gold  is 
scaly,  and  with  it  are  particles  and  scales  of  platinum  of 
the  same  shape  as  the  gold;  the  same  metal  occurs  in  the 
beach  sands  and  some  of  the  placers  of  California,  though 
no  platiniim  in  place  has  been  found  on  the  Pacific  Coast, 
Besides  the  gravel  in  the  bottom  of  the  stream  an  older 
series  is  exposed  loo  feet  above  it  interstratified  at  the  top 
with  a  white  silt  deposit.  This  deposit  is  a  delta  formed 
by  the  Tranquille  when  the  water  of  the  lake  was  at  a , 
higher  level,  in  times  following  the  glacial  epoch. 

The  gold  is  derived  from  eruptive  rocks  and  slates,  and 
the  best  paying  ground  is  where  the  creek  crosses  a  belt  of 
soft  slates.  In  some  cases  the  pay  is  derived  from  a  cement 
consolidated  by  calcareous  matter  resting  upon  rotten  slate. 
Gold  is  found  in  gravels  resting  on  the  surface  of  the  older 
rocks  in  irregular  pockets  and  uneven  hollows,  and  again 
it  is  not  till  these  gravels  are  found  spreading  more  widely 
and  in  thicker  masses  over  the  Tertiary  beds  that  the 
richer  gold  deposits  occur.  The  rocks  underlying  the 
Tertiary  formations  are  decomposed  and  shattered  and  pass 
upward  into  a  clayey  breccia  followed  by  clays  and  shales. 


219 


The  natural  history  of  Cherry  Creek  is  instructive  as 
typical  of  how  placer  valleys  and  deposits  are  formed. 

The  actual  valley  of  the  stream  is  at  the  productive 
part  a  narrow  depression  scoring  the  bottom  of  a  deeply 
rounded  valley.  This  valley  existed  and  carried  a  stream 
like  the  present  in  pre- glacial  times.  When  the  glacier 
from  the  gold  range  retreated,  leaving  the  valley  blocked 
with  morainal  matter  and  boulder  clay,  the  stream  again 
began  excavating  its  bed  down  the  valley.  Soft  materials 
were  rapidly  removed.  The  stream  at  first  changed  its 
bed  frequently,  but  at  last  subsided  into  the  deep  narrow 
valley  in  which  it  now  flows,  cutting  a  new  course  in  the 
rock  of  the  wide  valley  and  leaving  the  old  channel  yet 
buried  with  drift  on  one  side  of  the  present  valley. 

The  best  paying  claim  is  situated  on  a  little  bench  30  feet 
above  the  stream.  Indians  o1)tained  gold  from  the  veins 
by  lighting  fires  over  them  and  dashing  cold  water  on  the 
heated  rock,  thus  disintegrating  the  rock  and  exposing  the 
metal. 

Placer  grounds  extend  over  100,000  square  miles  of 
Lower  Canada.  The  gravels  are  generally  covered  by  a 
layer  of  vegetable  earth  or  by  a  bed  of  clay.  They  lie 
on  Lower  Silurian  diorite  and  scrpctitine  gold-hcaring  rocks, 
as  in  the  Ural  Mountains  of  Siberia;  hence  Russian  engi- 
neers consider  that  the  gold  originates  from  the  rusty  quartz 
of  the  crystalline  schists  in  the  vicinity  of  serpentines  and 
diorites.  Diorite  in  appearance  is  commonly  a  greenish- 
gray  rock  speckled  over  with  little  white  crystals  of  feld- 
spar and  often  too  with  crystals  of  hornblende  or  mica. 
From  the  alteration  of  the  hornblende  it  derives  its  green- 
ish-gray color,  and  hence  is  often  called  "  greenstone," 
while  its  speckled  character  would  name  it  by  miners  as  a 
porphyry.  Diorite  is  in  many  countries  an  accompani- 
ment of  gold,  or  gold-bearing,  particularly  in  Northwestern 
America,  where  it  is  often  associated  with  serpentine.  The 
latter  is  commonly  a  green  streaky  rock  like  green  marble, 
and  is  often  the  result  of  alteration  of  volcanic  rocks  and 
others  containing  magnesian  silicate  minerals;  hence  the 
frequent  association  of  serpentine  with  eruptive  rocks. 
Both  serpentine  and  diorite  are  imijinant  factors  in  the 
gold-bearing  zone  of  the  Northwestern  and  Pacific  Coast 
areas. 


230 


i 


Where  the  Chaiulieve  River  makes  sharp  turns,  Rold  is 
foxincl  in  cavities  and  fissures  of  the  clay  slates,  which  run 
in  parallel  ridges  and  are  uncovered  at  low  water,  when 
miners  break  it  up  and  search  the  slates  to  a  depth  of  sev- 
eral feet.  The  fissures  are  filled  with  a  clay  gravel  which 
carries  the  gold.  Many  hundreds  of  dollars  have  been  ex- 
tracted from  between  the  layers  of  slate.  The  gold  is 
sometimes  tarnished  by  a  black  coating  of  manganese.  At 
Devil's  Rapids  the  gold  lies  in  a  bed  200  feet  thick  of  a  hard 
alluvial  conglomerate  cemented  by  clay.  The  Des  Plantes 
River  runs  over  serpentine,  diorite,  and  schist  yielding 
grains  of  gold  mingled  with  black  sand.  The  gold  occurs 
in  the  re-entering  angles  and  cracks  of  the  diorite.  In  some 
streams  in  Lower  Canada  most  of  the  gold  is  extracted 
from  fissures  in  the  sandstone  bed-rock  to  a  depth  of  five  or 
six  feet.  In  the  joints  and  lamina  where  gravel  has  pene- 
trated and  indurated,  gold  is  found  in  the  largest  masses  in 
abundance.  The  worn  appearance  of  the  gold  implies  that 
its  source  is  remote.  When  gravel  lies  on  blue  clay  with 
boulders  in  it  in  this  region,  it  is  poor,  but  becomes  richer 
when  resting  on  bed-rock.  In  two  layers  of  gravel  sep- 
arated by  a  stratum  of  clay  the  lower  only  is  gold-bearing. 
These  clays  are  barren  but  contain  cubic  pyrites,  pebbles, 
black  sand,  and  garnets.  The  layers  of  gold-bearing  allu- 
vion are  not  continuous,  but  occur  in  sheets  or  belts  of 
variable  extent  and  thickness.  The  gold,  too,  occurs  in 
patches,  isolated  or  remote  from  one  another.  A  week's 
work  at  a  good  spot  is  often  better  than  months  in  poor 
ground.  Quartz  veins  in  Lower  Canada  run  in  the  direction 
of  the  stratification,  northeast  by  southwest,  often  ob- 
scured by  vegetable  soil,  and  require  prospecting  by 
trenches  as  at  Cripple  Creek,  Colorado  and  many  other 
regions. 

The  veins  conta'n  pyrite,  zinc  blende,  galena,  and  native 
gold.  The  pyrite  and  blende  carry  the  gold,  which  is  de- 
rived from  lower  Silurian  rocks.  These  veins  occur  in  soft 
blackish  schists  and  greenish-gray  rocks,  or  in  fine-grained 
felsite  trap  or  indurated  volcanic  ash  with  seams  and  stains 
of  green  epidote.  The  latter  is  a  grass-green  mineral  often 
found  associated  with  quartz  and  mineral  veins,  and  with 
iron,  garnets,  and  hornblende.  It  is  a  secondary  mineral 
derived  from   iron-bearing  minerals  such  as  hornblende. 


331 

etc.  ftomctitncs  it  occurs  in  distinct  crystals,  but  uioro 
commonly  as  a  v;tass-}^rcen  staininj;  t<»  the  rock.  The 
prospector  is  likely  t)ften  to  come  across  this  mineral  in 
his  searches  among  the  crystalline  rocks  and  veins.  It  is 
no  particular  sign  of  the  presence  or  not  of  precious  metals, 
but  a  common  accf)mpaniment  of  them;  it  is  much  lighter, 
more  grassy-green  than  copper  carbonate. 


e. 


GOLD    IN    SI.ATES. 

In  all  parts  of  the  slaty  belt  quartz  veins  abound.  A 
band  of  slates  is  often  characterized  by  small  thin  streaks 
of  quartz  and  lenticular  bunches  through  all  its  layers  with- 
out showing  any  well-defined  large  veins.  The  quartz 
holds  little  pyrite.  Good  pay  is  obtained  by  cleaning  up 
the  bed  of  the  river  itself  and  by  crevicing  in  potholes, 
pockets,  fissures,  or  slates,  or  sides  of  the  valley.  In  Leech 
River,  the  gold  was  generally  diffused  in  small  quartz  seams 
through  certain  parts  of  the  slaty  rocks,  of  which  a  great 
mass  was  worn  down  in  excavating  the  valley,  leaving 
the  heavy  gold  by  natural  process  of  concentration  in  a  nar- 
row line  on  the  bottom  of  the  excavation.  Copper  ores  and 
gold  in  some  localities  are  associated,  especially  where 
diorites,  green  slates,  and  dolomites  are  extensively  devel- 
oped. Gold  has  been  obtained  from  "  gossan,"  or  surface 
float  filling  the  crevices  in  a  cavernous,  rusty  dolomite. 

Dolomite  is  a  magnesian  limestone,  the  carbonate  of  lime 
of  an  ordinary  limestone  replaced  in  a  great  measure  by 
carbonate  of  magnesia.  As  magnesian  carbonate  takes 
less  place  or  volume  than  carbonate  of  lime,  the  replace- 
ment often  gives  by  shrinkage  a  minutely  cavernous  in- 
coherent structure  to  the  dolomite  limestone.  And  just 
such  a  structure  is  that  of  which  metal-bearing  solutions 
are  liable  to  take  advantage  and  to  deposit  in  it  their 
metals;  as,  for  instance,  the  silver-charged  dolomites  of 
Leadville  and  Aspen,  Coloudo.  A  gold  copper  vein  at 
Palmerston  carries  much  copper  pyrites;  it  is  associated 
with  dark  greenish  hornblende  rocks  and  slates,  and  the 
gangue  is  a  translucent  quartz  divided  into  layers  or  rib- 
bons by  strings  of  iron  and  copper  pyrite  and  calcspar. 
The  last  mineral  is  sometimes,  but  not  commonly  a 
gangue  of  metalliferous  veins. 


a  J  2  ' 

Gold  veins  occur  near  Lake  Ontario  in  fissures  in  syenitic 
granite,  tliat  is,  in  granite  containinj^a  good  deal  of  horn- 
blende as  well  as  mica,  with  micaceous  and  talcose  slates 
forming  the  walls  and  horses  in  the  veins.  The  talcose  or 
soft,  greasy,  greenish  soapstone-like  slates  result  from 
chemical  decomposition  of  the  sy«'nite  along  the  sides  of 
th"  fissure,  apparently  a  sort  of  indurated  gouge  or  selvage 
to  the  ([uartz  vein  containing  gold-bearing  arsenical  pyrites. 
Tliesj  veins  are  irregular  in  t'lickness  and  quality,  the 
fiss.iic  opening  out  wide  in  some  places  and  pinching  in 
others,  and  the  ore  richer  in  places  than  in  others.  Diorite 
is  associated  with  some  of  these  veins  like  the  "porphyry 
contacts"  of  Colorado.  All  over  the  glacial  drift  of  the 
plains  from  Lake  Manitoba  to  the  Rockies  gold  is  more  or 
less  present,  and  appears  to  have  been  washed  from  the 
shingle  terraces  along  the  eastern  base  of  the  mountains 
where  it  is  believed  the  precious  metal  is  most  abundant. 
On  the  Saskatchewan  small  red  garnets  and  black  or  mag- 
netite sand  form  the  bulk  of  the  residue  of  the  pannings. 
The  gold  is  not  derived  so  directly  from  the  mountains 
themselves  as  from  the  drifts  of  granitoid  pebbles  spread 
over  the  face  of  the  country,  derived  from  the  denudation 
of  the  great  belt  of  Laurentian  rocks  extending  from  the 
shores  of  Lake  Superior  northwest  to  the  Arctic  Sea.  Li 
New  Brunswick  gold  is  found  in  the  pebbles  composing 
the  Carboniferous  conglomerates  of  the  coast.  Gold  veins 
also  occur  in  diorite;  some  are  short  gash  veins. 


NFAVKHNIH.ANI)    AND    NOW    SCOTIA     (WJLD. 

In  Newfoundland  quartz  veins  occur  in  serpentine  of  the 
Lower  Silurian,  and  where  serpentine  is  absent  there  is  no 
ore.  It  occurs  in  pockets  rather  than  veins.  Small  veins 
intersect  one  another,  forming  a  knot  or  bow,  at  point  of  in- 
tersection often  rich  in  gold.  The  rock  is  a  dark-green 
chlorite  schist.  In  Nova  Scotia  the  gold-bearing  series  is 
in  Cambrian  greenish-gray  grits  and  sandstones  with  bands 
of  shale  overlaid  by  black  earthy  pyritous  slates  and  sandy 
beds  much  crumpled  and  contorted.  The  lodes  are  in  the 
most  metamorphosed  quartzitic  rocks  and  in  soapstone 
with  rutile  and  garnets.  These  strata  are  thrown  into 
waves  (Plate  CIII),  the  elevated  points  of  which  having 


1  'jen  plani'd  off  show  the  Rohl-brnrinj;  fpmrt/  \(h\vs  in  the 
l-rni  of  irrogular  ellipses,  tinld  occurs  as  spots  aiul  himchos 
»'P  to  6o-()Z.  nuj(^;ets,  'I'hc  leads  confonii  with  the  strati- 
fication. It  is  alleged  that  much  ol  the  ^old  dritt  of  Nova 
Scotia  has  been  carried  into  the  Atlantic  to  form  the  sub- 


fi$9  OOLusov  ammtmmtm  ms  li«r«v  «••«« 


I'l.ATK  cm. 

Contorted  (jold  Veitis  m  Hit- Ciiribcii  iJistriil,  Novn  .SluIih.     ( Locke. > 

marine  banks  of  the  coast.  Copper  Lake  is  a  curious  in- 
stance of  ^old  occurrence.  The  lake  was  drained.  A  layer 
of  tough  clay  and  }<lacial  drift  was  met  underneath  the  mud 
and  vegetable  matter,  and  in  this  under-clay  small  round 
nuggets  were  often  found.  Irregularities  in  veins  some- 
times disappear  with  depth.  Lenticular  veins  may  die  out 
before  reaching  the  surface,  but  with  depth  may  resume. 


CHAI'TlCk    XVIL 


CALIFORNIA. 


California  has  many  characteristics  common  to  the  North- 
western field, — the  same  general  mountain  features,  the 
same  peculiar  set  of  gold-bearing  strata,  and  the  same 
characteristic  placers,  some  of  which  are  a  little  difTerent 
from  placers  in  general  by  being  covered  with  heavy  flows 
of  lava.  The  country  is  divided  into  three  great  belts: 
One  the  Sierra  Nevada  range,  a  second  50  miles  west  of 
this  main  axis,  principally  including  the  great  valley  sys- 
tem, and  the  third  the  Coast  range.  The  Sierra  is  the  belt 
of  intrusive  granite  and  of  Mesozoic  strata  intensely  altered 
by  heat.  The  great  valley  is  the  belt  of  alluvial  deposits, 
and  the  Coast  range  is  a  fold  of  Tertiary  and  Cretaceous 
rocks  also  much  crystallized  and  altered  by  heat.  The 
Sierra  is  the  belt  of  the  origin  of  the  precious  metal  in 


224 

place  in  veins;  tbe  Coast  ranjj^es,  of  quicksilver,  cinnabar, 
usphaltum,  etc. ;  the  j^reat  vall<,'y,  of  gold-bearing  alluvia 
which  also  cover  poi  lions  of  the  Sierras.  In  the  Sierras 
volcanic  activity  has  ceased,  but  on  the  Coast  ranges  solfa- 
taric  action  is  still  apparent.  The  coast  ranges  are  of 
shales  and  sandstones,  and  limestones  altered  by  metamor- 
phic  heat  into  crystalline  quartzites,  slates,  and  sometimes 
serpentine  and  marble:  volcanic  rocks  appear  often,  and 
granite  but  rarely.  The  slates  are  changed  into  jaspers 
and  serpentines  which  carr'-  the  cinnabar. 

In  the  Temescal  range,  which  is  composed  of  granite, 
porphyry  and  metamorphosed  sandstone  of  Cretaceous  and 
Tertiary  origin,  is  one  of  the  few  localities  in  North 
America  where  tin  has  been  discovered.  Large  areas  of 
the  Coast  range  are  covered  with  lava,  pumice,  and  ob- 
sidian.    Hot  springs  and  sulphur  beds  occur. 

The  geological  structure  of  the  Sierra  Nevada,  according 
to  Bowie,  is : 

1.  A  central  intrusive  core  of  granite  flanked  by 

2.  Metamorphic  slates  of  Triassic  and  Jurassic  age  com- 
posing the  gold-bearing  slate  formation,  overlaid  by 

3.  A  covering  of  Cretaceous,  Tertiary,  and  Post-Tertiary 
deposits  which  are  either  river  deposits  forming  the  gold 
placers,  or  sedimentary  volcanic  layers,  or  lava  or  marine 
formations. 

Granite  occurs  in  the  northwest  part  of  the  State,  dis- 
appearing in  the  northeast  under  great  lava  beds,  and 
reappearing  in  Butte  and  Plumas  counties,  increasing  in 
mass  and  importance  to  the  south. 

The  gold-bearing  slates  are  metamorphic,  crystalline, 
clayey  chloritic,  and  talcose  slates  occupying  the  western 
slope  of  the  Sierras,  with  occasional  areas  of  granite  en- 
closed in  them.  In  this  slate  occur  the  veins  of  quartz  carry- 
ing gold.  Some  veins  are  vory  large  and  traceable  for 
vast  distances;  others  are  small  and  short  lenticular 
bodies. 

Diorite  and  serpentine,  as  throughout  the  Pacific  Coast 
field,  are  often  associated  with  gold  vein  deposits.  Basaltic 
tufa  is  generally  of  a  light  greenish  or  yellowish  color  or 
rusty,  and  contains  angular  quartz  pebbles.  The  gold  de- 
posits of  sand  and  gravel  rest  upon  the  tufa,  and  in  Stanis- 
laus County  are  not  capped  by  lava.     Bones  and  teeth  of  the 


aaS 


elephant  are  found.     An  average  section  of  a  placer  in  this 
district  is  as  follows: 

1.  Top  soil,  red  sand. 

2.  Coarse  red  granite  gravel  and  sand. 

3.  Red  cement  (hardpan). 

4.  Sand  and  pebbles. 

5.  Loose  yellow  sand. 

6.  Dark  colored  gravel  containing  fragments  of  slate,  gran- 

ite porphyry,  greenstone,  serpentine,  quartzite,  diorite, 
materials  derived  from  the  Sierra  Nevada. 

Total,  about  50  feet. 

The  greater  part  of  the  gold  is  confined  to  the  lower 
stratum  of  gravel  next  to  bed-rock  associated  with  mag^netic 
iron  (black  sand)  and  platinum. 

Lava  covers  many  thousands  of  square  miles  of  Northern 
California  and  Southern  Oregon,  and  buries  up  many  a  valu- 
able area  of  gold  placer  ground.  The  latter  are  limited  to  the 
North  in  accessibility  by  the  overwhelming  shell  of  lava. 
Sedimentary  layers  of  fragments  of  lava  carried  to  a  dis- 
tance by  water  and  deposited  as  breccia  or  conglomerate  of 
volcanic  ashes  are  found  interstratified  with  the  gold  gravels 
or  covering  them.  The  gravel  deposits  vary  in  texture  from 
a  fine  pipe-clay  to  sand  and  coarse  gravel,  and  from  that  to 
boulders  weighing  tons.  These  deposits  were  laid  down  by 
the  action  of  Tertiary  rivers  which  had  the  same  general 
course  as  the  present  streams  on  the  west  slope  of  the  Sierras, 
but  whose  channels  were  wider  and  slopes  greater.  These 
rivers  eroded  the  gold-bearing  slates  with  their  quartz 
veins  and  concentrated  the  gold  in  deposits  often  300  feet 
wide  at  bottom  and  several  thousand  feet  wide  at  top,  with 
a  depth  now  varying  from  a  few  inches  to  600  feet.  Volcanic 
eruptions  have  in  places  covered  these  deposits  with  lava 
and  tuff  hundreds  of  feet  deep.  Quantities  of  fossil  wood 
and  remains  of  land  and  water  animals  found  in  these  de- 
posits attest  their  river  fresh- water  origin. 

The  top  gravel  sometimes  pays  but  not  generally.  Gold 
may  also  be  found  at  times  literally  in  grass-roots  entangled 
in  the  roots  of  the  plant.  But  the  best  pay  is  generally 
near  or  at  bed-rock.  Where  bed-rock  is  of  slate  upturned 
on  its  edges,  gold  frequently  permeates  it  a  foot  or  two,  so 
a  miner  does  not  stop  till  he  has  dug  up  some  bed-rock. 
Fine  sand  is  generally  poorer  than  coarse  gravel.     Deep 

25 


!  r 


226 

pot-holes  filled  with  sand  are  often  but  not  always  rich. 
All  this  goes  to  show  that  to  prove  a  placer  a  system  of 
sluicing  should  be  adopted  which  bottoms  the  entire  deposit. 

BEACH    MINING. 

Beach  mining  is  carried  on  in  various  places  along  the 
coast  especially  between  Cape  Mendocino  in  California  and 
the  Umpqua  River,  Oregon.  The  beach  sands  contain  gold 
in  a  finely  divided  state  in  layers  (one  or  two  feet  deep)  of 
magnetic  iron  sand,  which  by  concentrating  action  of  waves 
and  tide  is  separated  from  the  lighter  quartz  sand.  By  the 
wash  of  the  water  the  gold  layers  are  sometimes  exposed 
and  sometimes  covered  by  the  non-auriferous  material. 
With  the  gold  platinum  is  found  in  flakes,  like  the  gold  only 
more  compact.  As  the  tides  continually  alter  the  position 
of  the  gold-bearing  layers,  it  is  necessary  to  prospect  daily 
for  the  richest  spots,  which  are  generally  covered  at  high 
water.     The  sand  assays  from  $5  to  $10  to  $30. 

DEEP    LEAD    MINING    AND    MOTHER   VEINS. 

Gold,  in  this  State,  is  often  mined  in  deep  deposits  over- 
lain by  lava,  by  tunnels  and  drifts.  Where  a  pay  channel 
has  been  found  or  is  supposed  to  exist  a  prospecting  tunnel 
is  driven  in  to  find  and  develop  it.  Whenever  the  nature 
of  the  deposit  admits  it,  hydraulicking  is  the  best  method. 
The  great  mother  veins  or  congeries  of  veins  of  California 
are  extraordinary  phenomena.  That  of  Nevada  and  Amador 
is  an  irregular  disjointed  outburst  of  quartz  extending  80 
miles  from  Mariposa  to  Amador.  In  a  series  of  lenticular 
bodies  separated  by  barren  intervals,  it  occupies  a  width 
of  12  miles,  and  the  mines  are  located  on  intermittent  out- 
bursts of  quartz.  One  of  these  veins  8  to  40  feet  wide  sud- 
denly pinches  out  in  500  feet.  Free  gold  averaging  $10  to 
$15  and  pyrite  are  the  constituents.  These  veins  are  in 
slate.  In  the  higher  portion  near  the  junction  of  slates  and 
granite  are  isolated  patches  of  ancient  gravel  capped  with 
lava.  Some  of  these  veins  change  with  depth  into  tellurides 
as  at  Cripple  Creek,  Colo.  In  El  Dorado  the  belt  of  gold- 
bearing  slates,  etc.,  is  30  miles  wide.  Some  mines  noted  for 
free  gold  near  the  surface  ceased  at  250  feet,  passing  into 


227 


to 


barren,  poor  quartz.  Diorite,  slates,  schintH,  greenstones, 
syenite  and  serpentine  make  up  their  gold  fonnati  »n.  The 
greenstones  seem  responsible  mainly  for  the  gold  here.  Gold 
is  generally  sparingly  distributed  in  the  gangue,  but  rich  in 
the  pockets  at  intervals.  Veins  are  comnioiily  narrow 
though  plentiful,  and  demand  economic  mAnugetnent. 

The  dolomitic  or  magnesian  portion  of  the  great  mother 
lodes  decomposes  readily  and  becomes  a  rusty  vtllular 
"  gosscn"  traversed  everywhere  by  seams  of  white  quartz 
which  carry  the  gold  values.  The  rich  gravel  belt  is  coex- 
tensive with  the  gold-bearing  slates  and  is  derived  from 
them.  The  coarse  gold  lies  nearest  the  place  where  it  origi- 
nated. The  lenticular  veins  are  rather  intercalated  heds 
or  bodies  between  the  stratification  than  true  fissure  veins. 
The  rocks  in  many  localities  are  penetrated  in  every  direc- 
tion by  little  irregular  veinlets.  Spots  are  rich  even  where 
not  more  than  one  inch  thick. 

The  character  of  the  gold  varies  in  form  and  value.  It 
is  coarse  and  in  flat  grains  on  bed-rock;  in  the  upper  jmrt 
of  the  bank  "  flour"  and  scaly  and  50  cents  purer  than  the 
coarse.     Lumps  occur,  coarse  and  scraggy. 

Coarse  gold  also  is  generally  well  rounded  and  smooth, 
the  finer,  more  flaky  with  occasionally  quartz  ttdljeritig  to  it. 
If  coarse  gold  is  worth  $17  fine  gold  is  worth  $18  per 
ounce. 

A  system  of  mining  is  carried  on  called  "  seum  dig- 
gings;" this  is  on  decomposed  bed-rock  filled  with  irreg- 
ular seams  of  quartz  containing  gold.  These  rocks  are 
commonly  soft  slates  or  sandstones  filled  with  iron  pyrites 
traversed  by  little  quartz  veins  and  serpentines.  These 
veins  are  like  the  German  stockwerks,  a  multitude  of 
little  veins  ramifying  in  all  directions  with  gold  far  fn^m 
uniformly  distributed  in  them,  mostly  in  pockets.  In  these 
a  miner  may  make  nothing  or  a  fortune,  or  strike,  as  one 
did,  a  $4,000'  nugget.  When  these  quartz  seams  leave  the 
soft  decomposed  matrix  and  pass  into  hard  rock  they  run 
out  or  disappear  altogether,  and  gold  invariably  gives  out. 
Veins  occur  as  bunches  of  quartz  quite  thick  or  split  into 
eight  or  ten  strings  which  disappear  before  reaching  the 
surface.  Quite  a  number  of  quartz  seams  found  below  do 
not  extend  to  the  surface.  On  the  other  hand  the  great 
mother  lode  of  California  outcrops  in  places  like  M\  im- 


'!* 


228 

mense  white  wall  60  feet  wide.  The  likeliest  vein-stone  is 
seamy,  oxidized,  rusty,  mottled,  and  marbly.  The  gangue 
of  some  veins  is  crystalline  quartz,  semi-transparent  and 
ribboned  in  such  a  way  as  to  present  the  appearance  of  a 
succession  of  layers  parallel  to  the  walls,  one  of  these  layers 
or  lamina  being  more  productive  than  another.  These 
bands  may  be  separated  from  one  another  by  thin  layers 
of  quartz  differing  in  color  from  that  forming  the  seams 
themselves,  or  again  laminae  of  slate  may  divide  the  vein 
into  bands  no  thicker  than  paper.  Very  crystalline,  pure, 
transparent  quartz  is  "  hungry"  or  poor,  while  if  oxidized 
and  showing  the  square  little  hollows  left  by  the  cube  of 
pyrite  that  has  oxidized  out  it  is  liable  to  break.  Below 
the  drainage  line  of  oxidation  the  ore  is  liable  to  be  hard  of 
treatment. 

Flakes  of  gold  are  distributed  in  the  vein-stone  in  the 
vicinity  of  certain  dark-colored  streaks  parallel  to  lines  of 
deposits  of  quartz.  When  the  gold  lines  a  crystalline  cav- 
ity it  is  in  well-formed  crystals.  In  narrow  fissures  the 
crystals  are  flattened  to  plates.  Besides  quartz,  semi-opal 
and  chalcedony  occur  interleaved  between  layers  of  quartz, 
showing  clearly  their  origin  from  hot-spring  action.  Some 
California  lodes  have  been  worked  to  a  depth  of  1,500  feet 
without  impoverishment.  Bodie  in  Mono  County  is  an  iso- 
lated mass  of  porphyry,  the  centre  of  a  great  eruption. 
There  are  evident  traces  of  igneous  action  comparatively 
recent  in  Mono  Lake  with  islands  of  lava.  The  surface  of 
the  mountain  is  covered  with  an  ochreous  earth  derived 
from  decomposing  porphyry  and  containing  fragments  of 
quartz,  jasper  and  chalcedony  derived  from  the  breaking 
up  of  various  veins  and  lodes  which  intersect  the  mountain, 
while  parallel  veins  of  hard,  compact,  uncrystalline  "  hun- 
gry" quartz  occur  on  the  surface  of  the  hill ;  at  a  depth  of 
50  feet  they  become  softer  and  are  productive.  The  veins 
show  a  fine  parallel  ribboned  structure  indicative  of  their 
deposition  by  hot  springs  like  those  at  Steamboat  in 
Nevada. 

YUBA   AND   OTHER   PLACERS. 

The  Yuba  placer  is  a  good  typical  one  of  a  certain  kind 
of  placer.  It  is  composed  of  250  feet  of  gravel  protected 
by  lava  and  cemented  into  a  hard  conglomerate.     The 


t  i 


Hi 


229 


ind 
;ed 
"he 


colors  of  the  upper  and  lower  portion  of  the  mass  differ,  due 
to  oxidation  of  iron  pyrites  by  surface  waters  staining  the 
gravels  red  and  brown  in  undulating  lines  contrasted  with 
the  blue  color  of  the  unoxidized  detritus.  The  "blue 
gravels"  are  highly  impregnated  with  iron  pyrites,  forming 
a  cement.  Isolated  patches  of  fine  sand  exhibiting  false 
bedding  occur  in  the  upper  portions  and  contain  much  fossil 
wood  flattened  by  pressure  and  blackened  to  coal.  When 
covered  by  lava  this  wood  is  beautifully  agatized.  On  bed- 
rock the  grains  and  scales  of  gold  are  very  conspicuous  and 
are  inlaid  so  firmly  upon  the  hard,  smooth  granite  bed  of 
the  ancient  river  as  to  resemble  a  gilt  mosaic.  Beneath 
the  lava  of  Table  Mountain,  Tuolumne,  is  a  fine-grained 
sandstone  interstratified  with  seams  of  clay  and  argilla- 
ceous shale.  With  these  are  beds  of  strongly  cohering 
conglomerate  or  cement,  at  bottom  of  which  is  the  pay 
gravel. 

DEEP    PLACERS. 

Professor  Eggleston,  on  California  deep  placers,  says: 
"  The  great  lava  flow  filled  the  deep  channels  and  cov- 
ered elevations  also.  The  Yuba  cuts  canyons  through  the 
volcanic  flow  to  a  depth  of  3,000  feet,  showing  in  section  : 
first,  lava ;  second,  gravel ;  and  third,  slate.  The  deep  leads 
were  found  by  miners,  who  could  not  get  hold  of  the  open, 
easily  worked  placers,  and  so  were  driven  to  prospect  up 
hill  till  signs  led  them  to  a  point  underneath  the  lava. 
Deposits  are  sometimes  found  in  basins  formed  by  swelling 
of  the  bed-rock.  The  ancient  rivers  were  on  a  much  larger 
scale  than  now;  they  had  "bars,"  " eddies,"  rapids,  water- 
falls, with  gold  deposited  in  crevices.  There  were  long 
barren  stretches  and  pockets  of  richness.  Sometimes  there 
was  more  than  one  channel.  The  problem  of  drift  mining 
is  to  find  the  channels.  Some  of  the  best  drift  mines  have 
been  found  by  following  surface  placers  up  to  the  line  of 
disappearance  of  gravel  and  gold ;  at  this  point  is  a  channel 
and  place  to  prospect.  Sometimes  a  depression  in  the  line 
or  under  edge  of  the  country  rock  indicates  an  old  channel 
and  probable  presence  of  gold.  Gravels  are  not  confined 
to  definite  channels,  but  old  streams  sometimes  overflowed 
as  modern  ones  do,  carrying  gravel  and  gold  with  them. 
In  some  localities  two  distinct  sets  of  ancient  river  chan- 


230 

nels  have  been  found,  one  cutting  across  the  other,  very 
different  in  character,  showing  they  were  formed  at  different 
periods.  Gravels  sometimes  cover  the  whole  surface  of 
the  country  without  any  apparent  defined  channel.  Chan- 
nels are  subject  to  irregularities  and  are  sometimes  abruptly 
cut  oflF  by  faults  caused  by  a  movement  of  the  underlying 
pipe-clay  or  by  erosion  of  ground  beneath  the  flows." 

PROSPECTING    IN    IDAHO. 

The  southern  portion  of  Idaho  is  a  continuation  of  the 
sage-brush  and  alkaline  deserts  of  Nevada  and  Utah.  The 
Snake  is  the  principal  river.  The  valley  of  the  Snake  is  a 
plain  50  to  100  miles  wide,  covered  by  flows  of  recent 
basaltic  lava   (Plate  CIV.).     From  Wyoming  County  to 


3*^ 


Turn  OoLUmm  Kmmimmma  aho  ttarju,  mimmm. 


Plate  CIV. 

Great  Basalt  Plain  of  Snake  River.  Idaho,  with  Recent  Cones.     (After 

Locke.) 

Owyhee  County  north  of  this  plain  the  country  is  mountain- 
ous. This  northern  region  is  well  wooded  and  watered  and 
good  for  mining.  The  winters  are  long  and  severe.  A 
large  granite  area  occupies  part  of  Southwestern  Idaho, 
which  has  been  greatly  disturbed  by  eruptive  action  at  a 
comparatively  recent  date.  Dykes  of  basalt  occur  and  hot 
springs  abound,  issuing  sometimes  from  the  granite,  at 
others  near  volcanic  rocks,  showing  that  volcanic  heat  still 
remains  below  the  surface.  The  numerous  veins  in  the 
granite  strike  significantly  in  the  direction  of  the  ranges  in 
the  flanks  of  which  they  occur.  The  fissures  containing  the 
veins  were  made  by  the  upheaval  of  the  range.  The  move- 
ments in  the  ground,  the  fissures,  and  heat  action  probably 
belong  to  the  Snake  River  eruptions. 


2^1 

The  ores  were  probably  deposited  by  solfataric  hot 
springs  accompanying  the  eruption  of  basalt.  The  living 
hot  sprinjjfs  in  the  granite  are  charged  with  alkalies  and 
sulphohydric  acid,  and  may  be  called  modern  solfataras. 
These  occur  in  the  immediate  neighborhood  of  the  mines. 
As  we  have  often  before  said,  solfataric  action,  whether 
modern  or  extinct,  is  associated  with  ore  deposits.  And 
Idaho  seems  to  be  a  region  of  past  cs  well  as  present  vein 
formation  due  to  its  volca.?^c  character.  Some  of  the  veins 
are  faulted  and  their  walls  slickensided,  showing  that 
movements  have  occurred  oven  after  the  veins  were  formed 
and  filled.  And  veins,  like  old  healed  wounds,  being  weak 
places,  the  fissuring  again  took  place  along  the  old  breaks. 


BOISE    HASIN. 

The  gravels  of  Boise  Basin  cover  30  square  miles  to  a 
depth  of  12  feet,  representing  an  extensive  erosion  of  the 
upper  country  by  streams  far  greater  than  the  present  lim- 
ited rainfall  admits.  They  date  from  a  time  prior  to  some 
of  the  basalt  eruptions,  or  locally  the  gravel  is  covered  by 
a  basaltic  cap.     Some  veins  are  later  than  the  basalt  itself. 

The  mines  are  mostly  in  the  granite  or  veins  between 
granite  walls,  which  are  numerous,  rich,  and  narrow.  Some, 
like  the  celebrated  De  la  Mar  mine,  are  nothing  more  than 
rich  impregnations  of  decomposed  porphyry  dykes.  Ores 
carry  both  gold  and  silver,  the  gold  generally  free  or  in 
pyrites  or  zinc  blende.  Prospectors  should  carefully  ob- 
serve the  float,  the  character  of  the  croppings,  evidences 
of  disturbance,  and  especially  the  decomposition  of  the 
country  rocks,  particularly  if  that  rock  happens  to  be  a 
porphyry  dyke.  The  granite  masses  are  the  mother  of  the 
gold  mainly.  The  veins  here  often  grow  less  rich  with 
depth,  though  strong  veins  may  continue  rich  to  a  very  great 
depth,  and  decomposed  gold-impregnated  porphyry  dykes 
like  the  De  la  Mar  are  liable  to  continue  rich  to  as  great 
a  depth  as  the  decomposition  lasts. 

In  Wood  River  district,  ores  occur  in  granite  and  slate. 
The  placer  gold  gravels  are  of  great  volume  and  extent 
and  have  yielded  some  thirty  million  dollars.  There  are 
three  classes  of  gravel.  The  bars  of  Snake  River  are  gold- 
bearing,  but  the  gold  is  very  fine  or  "  flour." 


23i 

Rich  but  small  placers  occur  along  the  Salmon  River; 
small  placers  are  found  near  the  croppings  of  gold  veins, 
and  these  veins  have  been  discovered  by  following  up 
placers. 

The  deep  gravels  of  Boise  Basin  are  surrounded  by 
mountains  and  receive  no  drainage  from  beyond  the  basin's 
own  limits,  yet  it  contains  125,000,000  cubic  yards  of  placer 
material  250  feet  deep. 

Gravels  are  spread  over  the  whole  basin  and  occur  even 
on  the  tops  of  considerable  hills,  and  are  at  times  capped 
by  heavy  flows  of  basalt  as  in  California  "  deep  leads. ' 
The  pay  dirt  is  generally  on  bed-rock.  Large  boulders 
and  fossil  wood  are  abundant  here  as  in  California  placers. 
It  is  evident  that  a  great  river  once  flowed  through  the 
basin  and  transported  the  gold-bearing  gravels. 


CHAPTER  XVIII. 

MONTANA,  DAKOTA,  ARIZONA.  AND  NEW  MEXICO. 

This  is  a  region  of  granite  mountains  and  the  sources  of 
many  great  rivers.  The  geology  is  an  Archaean  granite  core 
with  patches  of  ancient  Paleozoic  sedimentary  rocks.  A 
large  portion  of  this  so-called  granite  is  really  an  eruptive 
diorite,  that  peculiarly  gold-bearing  rock.  It  is  composed 
of  augite,  hornblende,  and  plagioclase  feldspar  with  grains 
of  magnetite.  The  more  modern  eruptive  rock  called 
rhyolite,  usually  a  light-colored  gray  or  white  rock,  occurs 
as  well  as  porphyries.  Rhyolite  breaks  through  the  diorite 
granite  at  Butte  City.  The  prospector  sees  here  the  usual 
good  signs  for  a  mineralized  region,  viz.,  plenty  of  erup- 
tive rocks.  The  vein  material  is  simply  an  alteration  of 
the  country  rock  along  certain  places  in  which  calcite  quartz 
and  metallic  minerals  have  replaced  portions  or  all  of  the 
original  constituents.  There  is  no  definite  wall  generally 
to  the  ore  deposit,  at  least  on  one  side  only.  There  was 
no  pre-existent  open  fissure  of  the  same  width  as  the  pres- 
ent vein.  Gold  at  times  seems  merely  to  impregnate  the 
country  rock.  A  considerable  portion  of  the  ores  consists 
of  gold-bearing  pyrites  and  quartz  sufficiently  oxidized  to 


Wf 


233 

melt  freely ;  others  require  smelting.     A  good  deal  of  cop- 
per ore  is  present. 

The  placers  have  produced  richly.  The  deposits  are 
mostly  in  open  valleys  comparatively  high  upon  the  moun- 
tains, and  consist  of  coarse  gravel  varying  from  5  to  65  feet 
in  thickness.  Bones  and  tusks  of  elephants  have  been 
found  in  the  placers  of  the  glacial  epoch.  Bed-rock  is  not 
always  reached,  but  a  clayey  seam  or  false  bed  occurs,  below 
vhich  the  gravel  is  barren.  Alder  Gulch  is  the  most  noted 
placer ;  it  has  yielded  upward  of  thirty  million  dollars.  For 
a  distance  of  15  miles  from  the  summit  of  the  mountains  to 
the  Ruby  River  the  pay  has  been  continuous  and  rich. 
The  ground  is  worked  to  profit  along  the  banks  as  high  as 
the  water  can  be  carried,  and  is  known  to  be  rich  still 
above  the  highest  elevation  to  which  the  water  has  reached. 
In  Deer  Lodge  County,  where  the  first  discoveries  of  gold 
were  made,  the  ore  is  in  diorite  granite.  The  Butte  of 
Butte  City  is  a  rhyolite  lava  dyke.  The  ore  is  not  confined 
to  veins,  as  the  country  rock  often  yields  pay  material  for  a 
varying  distance  from  the  main  ore  body.  At  Heiena  the 
ores  are  mainly  gold-bearing  in  veins  in  granite  and  in 
slates.  The  veins  are  segregations  of  quartz  and  metal  in 
bodies  lying  parallel  with  the  formation.  At  Big  Hole  the 
river  for  ten  miles  runs  through  a  canyon  cut  in  gneiss  in 
which  are  abundant  gold-bearing  quartz  veins. 


PROSPFXTING    IN    DAKOTA. 

The  Black  Hills  of  Dakota  are  in  many  respects  geolog- 
ically an  epitome  of  the  great  Rocky  Mountain  system.  It 
is  a  wooded  island  rising  3,000  feet  above  the  ocean-like 
prairie.  It  is  an  independent  uplift  100  miles  distant  from 
the  Rocky  Mountains.  The  uplift  is  oval,  about  120  miles 
long  by  50  wide.  The  central  mass  is  granite  with  sedi- 
mentary rocks  of  all  ages  from  Cambrian  to  Tertiary,  dip- 
ping away  from  it  on  all  sides.  Large  veins  of  coarse  peg- 
matite granite  occur  in  the  granite ;  and  eruptive  rocks, 
porphyries,  etc.,  are  intruded  between  the  sedimentaries. 
The  hills  contain  iron,  copper,  tin,  gold,  and  silver.  The 
deposits  in  the  granite  and  schists  are  lenticular  in  shape 
and  composed  of  gold-bearing  pyrites. 

There  are  placers  of  stream  tin,  and  also  of  gold,  and  a 


i  i 


31  I 


remarkable  ancient  consolidated  placer,  found  at  the  base 
of  the  Potsdam  or  Cambrian  rocks  and  of  Cambrian  age. 
This  was  formed  by  the  ancient  ocean  advancing  upon  the 
slowly  sinking  granite  island,  sorting  over  the  material 
washed  from  the  land  and  depositing  it  as  sand,  gravel  and 
pebbles  as  the  basal  member  of  these  rocks.  The  particles 
of  gold  were  derived  from  the  granite  veins;  it  was  a  very 
ancient  primeval  gold  placer  now  consolidated  into  hard 
rock  as  shown  at  the  Homestake  mine.  It  forms  the  hard 
cement  beds  of  the  miner  and  is  stamped  as  an  ordinary 
free  milling  proposition.  We  have  called  attention  to  this 
before  as  an  instance  of  what  we  call  conglomerate  rock, 
rather  than  an  orthodox  modern  placer,  producing  gold. 

HOMESTAKE    MINE. 

In  the  sketch  (Plate  CV)  the  porphyry  cap  of  the  Home- 
stake  vein  is  shown.  The  porphyry  flowed  sometimes  be- 
neath the  Potsdam,  sometimes  on  it  and  beneath  the  Car- 
boniferous, sometimes  it  lifted  up  the  overlying  strata  by 
a  thick  intrusive  sheet.  The  lower  contact  line  is  the  old 
Potsdam  beach.  The  gold  in  these  ancient  placer  con- 
glomerates is  finer  than  that  in  the  veins,  as  is  commonly 
the  case  with  placer  gold.  The  Homestake  property  or  a 
section  6,000  by  2,000  feet  constitutes  the  gold  belt.  The 
deposits  were  of  course  originally  laid  down  as  beds,  but 
have  since  been  much  altered.  The  beds  contain  a  good 
deal  of  carbonaceous  and  graphitic  material,  which  were 
doubtless  relics  of  organic  substances  in  the  placer  which 
may  have  helped  in  precipitating  the  gold  and  chemically 
changing  the  iron  that  carried  it.  The  ore  is  not  continu- 
ous, but  in  great  "  shoots"  or  "  pipes"  of  a  lenticular  shape ; 
in  cross  section  the  shoots  cross  the  dip.  In  the  Home- 
stake  are  sheets  of  porphyry  cutting  across  or  parallel  with 
the  stratification.  The  influence  of  this  porphyry  on  the 
lode  is  good,  enriching  the  bed  and  by  oxidization  render- 
ing the  ores  more  free  milling. 

Mr.  W.  B.  Devereux  gives  a  very  interesting  and  in- 
structive account  of  these  peculiar  gold  deposits,  which  he 
aptly  calls  "  a  fossilized  placer : " 

"  The  underlying  rocks  are  metamorphosed  crystalline 
Paleozoic  schists  which   contain   the  gold-bearing  quartz 


liili 


>< 


^35 

veins.  Resting  unconformably  on  these  is  a  sedimentary 
formation  composed  of  debris  derived  from  the  schists 
containing  fossils  of  the  Potsdam  period.  The  base  of  this 
formation  is  a  conglomerate.  Gold  in  early  days  was 
found  in  the  lowest  stratum  of  this  conglomerate.  It  was 
obtained  by  horizontal  drifts,  and  many  hundred  thousands 
of  dollars  were  taken  out  in  a  short  time.  The  mines  were 
called  'cement'  mines;  the  conglomerate  needed  the  stamp 
mill  for  reduction.  This  conglomerate  merges  upward  into 
sandstone  or  quartzite.  It  is  a  mixture  of  quartz  boulders, 
pebbles  and  worn  fragments  of  schist  with  pebbles  of 
hematite.     Gold  occurs   in   tliis  both  as  mechanical  and 


Tm«  OOLutRv  KMaiummm  aho  MmrAi.  Mimmm, 


Plate  CV. 

The  Homestake  Mine,  Deadwood,  Black  Hills.     /',  Porphyry  ;  /),  Potsdam 
Conglomerate  ;  C.  Cement  Mines  ;  S,  Schist. 

chemical  constituents.  The  horizontal  character  of  the  sed- 
iments and  the  fact  that  their  fossils  belonged  to  saltwater 
types  shows  they  were  ocean  sediments  formed  in  shallow 
water  where  there  was  strong  wave  action.  These  depos- 
its were  later  overlaid  by  the  porphyry.  Ore  mined  from 
this  ground  milled  $50  per  ton,  and  the  stratum  lying  next 
bed-rock  was  exceedingly  rich.  Small  channels  and  depres- 
sions caused  local  concentrations,  and  these  channels  were 
followed  in  mining.  The  ore  was  hard  and  required  blast- 
ing. 

There  were  the  same  variations  of  quantity  as  in  ordi- 
nary placer  gravels.  Local  channels  showed  alternations 
of  rich  and  poor  material  due  to  diflferent  conditions  of 
current,  and  the  occurrence  of  the  greater  part  of  the  gold 
at  bed-rock  about  six  feet  thickness  as  a  rule  paid.     The 


236 

jfolcl  was  like  placer  f^oUl  in  shot  gold  or  smooth  rounded 
grains  slivjhtly  flattened.  The  cetnenting  material  was 
iron  oxide,  and  bed-rock  j^old  was  often  attached  to  the 
overlying  boulders  by  this  medium.  The  gold  was  most 
abundant  with  larj^e  cpiartz  boulders  or  pebbles  of  hema- 
tite. The  latter  nearly  always  carried  gold.  Each  grain 
of  gold  is  generally  covered  with  a  thin  coating  of  iron 
oxide  which  needs  a  blow  to  loosen  it.  The  richest  ore  is 
tiot  always  found  in  the  deepest  portion  of  the  channel  but 
sometimes  upon  one  slope.  Hasins  occur  in  these  channels 
which  are  rich.  They  seem  to  have  been  formed  by  whirl- 
pools." 

VVHiere  the  slate  was  soft  cement,  gold  worked  down  into 
the  crevices  for  several  feet.  The  history  of  these  singular 
deposits  appears  as  follows : 

"  The  gold  veins  were  in  existence  before  the  Potsdam 
period.  The  Potsdam  seas  washed  away. the  debris  result- 
ing from  the  disintegration  of  the  quartz  veins  and  depos- 
ited it  in  deeper  water  according  to  its  specific  gravity; 
at  the  same  time  gradual  wave  action  carried  the  gold  to 
bc'1-rock  in  the  same  manner  as  it  settles  in  a  miner's  pan. 
The  Homestake  vein  was  a  hard  reef  or  low  island.  In 
time  the  sediments  became  an  island  gradually  cementing 
into  rock,  until  later  eruptions  of  porphyry  caused  great 
local  metamorphic  action.  The  gold  now  became  partially 
dissolved  and  vvas  again  precipitated  as  thin  films  in  the 
schists  below.  A  period  of  rest  ensued  until  fresh-water 
streams  cut  through  the  upper  strata  and  disintegrated  the 
matrix  of  the  gold  and  afforded  material  for  a  new  concen- 
trating process.  This  disenveloping  process  has  continued 
to  the  present.  Gold  from  the  conglomerate  found  its  way 
to  the  bottom  of  IJeadwood  gulch  and  was  joined  with  sup- 
plies from  the  Homestake  vein  and  formed  the  great  Dead- 
wood  placer." 

The  gold  belt  is  a  zone  of  slates  and  schists  with  many 
lenses  and  shoots  of  ore.  Zones  impregnated  v/ith  pyrite 
pass  into  quartzites  forming  foot  and  hanging  walls.  Such 
deposits  have  to  be  worked  on  a  large  scale  to  pay,  and  con- 
centration and  chlorination  are  necessary. 

The  "  contact"  gold  deposits  carry  silver  also  and  vary  in 
thickness  from  a  few  inches  to  10  feet,  averaging  $15  to  $60 
in  value.     They  are  in  connection  with  igneous  intrusive 


111 


S!  M'i' 


rocks.  In  the  I'otsdatn  placrr  conKl<»niornti*  \hv  ^<A(\  oc- 
curs ahMivc  the  beddiiij^-platu-s  of  the  nak  ami  in  \trtical 
joint  planes  or  impreKnatinvj  the  qnartzite  and  replaiinj; 
the  cementinj;  material  of  the  original  sandstone  in  close 
connection  with  igneous  rocks.  On  the  surface  the  iron  is 
oxidized.  In  the  deeper  workings  a  bluish  (luart/ite  con- 
stitutes the  ore  ct)ntaining  minute  pyrites  occupying  spaces 
between  the  grains  of  sand  like  a  cetncnt.  The  ore  also 
occurs  in  large  bodies  replacing  i^cds  t)f  loose  shales 
which  occur  in  the  Potsdam.  The  porphyry  eruption  gave 
rise  to  hot  solutions  necessary  to  collect  and  recleposit  the 
gold  in  an  available  form.  The  Oro-Kino  mine  is  a  crater 
in  Archaean  granite  with  vertical  walls  filled  with  breccia. 
The  diameter  of  crater  is  130  feet.  The  breccia  consists 
of  angular,  worn  fragments  of  slate,  (|uartzite  and  porphyry, 
cemented  together  by  pyrite,  galena  and  blende  dcrivtd 
from  hot  ascending  solutions.  The  prospector  may  notice 
here  certain  good  concomitants  for  a  rich  lode.  viz.  :  the 
presence  of  eruptive  porphyry  and  close  to  it  a  loosely 
compacted  rock  or  breccia  supplying  good  places  in  its  in- 
terstices for  ore  solutions  to  circulate. 

The  outcrop  of  the  galena  deposits  is  lead  and  iron  car- 
bonate, but  with  depth  sulphides. 


TIN    DKPOSITS. 

The  Black  Hills  of  Dakota  have  long  been  noted  for  the 
occurrence  of  that  metal  so  very  rare  in  America,  viz.,  tin. 
Miners  in  1875  working  for  gold  found  a  troublesome  heavy 
black  sand  in  their  sluices.  Some  of  this  was  sent  to  Prof. 
Richard  Pearce  of  the  Argo  Works,  Denver,  and  found  by 
him  to  be  tin.  The  veins  carrying  tin  in  the  igneous  and 
granite  rocks  of  Harney's  peak  also  carry  gold  and  pyrites. 
It  is  probable  that  both  gold  and  stream  tin  were  derived 
from  the  Potsdam  sandstone.  The  veins  in  the  granite  arc 
a  chain  of  lenses.  They  vary  in  width,  some  being  upward 
of  100  feet.  When  tin  is  present  one  of  the  mineral  con- 
stituents of  the  granite  is  generally  wanting.  The  vein 
matter  is  composed  of  quartz  and  mica  alone,  or  of  soda, 
feldspar  and  mica,  or  of  pink  feldspar  and  quartz. 


238 


Tii 


MINERALS    ASSOCIATED    WITH    TIN. 

The  ICUa  tin  vein  is  columnar  and  oval,  150  feet  by  200. 
The  minerals  in  it  are  arranged  concentrically.  The  cen- 
tral portion  or  core  is  quartz  and  feldspar  surrounded  by 
albite  feldspar  and  mica  carrying  tin.  Another  zone  iiur- 
rounds  this  with  large  crystals  of  lithia  mica.  The  inter- 
stices between  these  crystals  are  filled  with  an  aggregation 
of  albite  feldspar  also  carrying  "  tin-stone,"  but  in  more 
massive  form.  Tourmalines  or  "  schorl"  also  occur  as  in 
tin-bearing  rocks  in  Cornwall.  Tourmaline  is  a  long,  jet 
black  crystal  not  unlike  hornblende.  The  common  mica 
associated  with  these  tin  deposits  is  of  alight  greenish  yel- 
low color,  and  the  feldspar  is  white.  When  mica,  quartz 
and  feldspar  are  all  present  in  the  granite,  tin  is  absent; 
when  only  mica  and  quartz,  tin  is  present.  If  the  vein  is  of 
feldspar  alone  there  is  no  tin.  The  quartz  is  usually 
banded.  If  the  crystals  of  the  rock  are  large  the  tin  crys- 
tals are  large  also.  Tin  occupies  interstices  between  crys- 
tals. Apatite,  columbite,  beryls,  garnets,  barytes,  zircon, 
corundum  minerals  also  occur.  Stream  tin  is  not  so  pure 
as  the  vein  tin.     The  yield  is  about  74  per  cent.  tin. 

For  (Hir  knowledge  of  the  deposits  of  the  Black  Hills  we 
are  indebted  mainly  to  Prof.  F.  C.  Carpenter's  admirable 
report. 

I'ROSI'ECriNC.    I'OR    I'l.ACER    DEI'OSITS    IN    l>AK<)TA. 

E.xperiences  in  this  region  with  the  gravels  as  related  by 
Jenny  are  very  suggestive  to  the  placer  prospector. 

"  Tlie  placer  gravels  result  from  decomposition  and  ero- 
sion of  the'  rocks,  and  these  included  gold  deposits  in  Ter- 
tiary times.  The  gravel  deposits  of  French  Creek  show  a 
local  rich  concentration  of  gold  on  the  outer  edge  of  the 
bed-rock.  Though  very  encouraging  at  first,  on  driving  an 
open  cut  into  the  bar  where  the  gravel  was  undisturbed  the 
richness  of  the  pay  dirt  rapidly  decreased  and  soon  bec'iiiit 
uniform,  showing  the  result  .irst  obtained  was  only  a  super- 
ficial rim  rock  'prospect.'  The  richest  layer  was  rarely  ov 
bed-rock,  but  10  to  20  feet  above  it  in  a  sort  of  false  bottom 
of  compact  clayey  gravel  which  had  retained  most  u£  the 


Ilii 


'39 


lit 


lie 


gold.  The  gold  was  in  flattened  scales  free  from  black 
sand  but  associated  with  little-worn  garnet  crystals.  The 
gold  is  derived  from  quartz  ledges  in  schists  rather  than 
from  the  intruded  granites,  as  shown  by  the  fact  that  the 
gulches  paved  wholly  with  granite  were  barren.  Pay 
gravel  is  of  heavy  pebbles,  clayey  sand,  and  many  garnet 
crystals  derived  from  the  schists.  It  is  soft,  rarely  cemented 
to  a  conglomerate,  and  easily  washed  in  a  sluice.  There 
was  a  general  diffusion  of  gold  in  the  creek  beds  but  little 
concentration  in  rich  deposits,  due  to  slight  denudation  of 
the  ledges  and  want  of  sufficient  grade  in  the  valley  to 
cause  a  concentration  of  gold  into  a  paying  channel.  Down 
Spring  Creek  where  a  large  quartz  vein  crosses  the  gulch, 
gold  is  found  in  the  stream  bed,  derived  from  a  decomposed 
stratum  of  clay  slate  which  retained  the  gold  swept  over 
it  from  the  quartz  vein.  It  is  noticeable  that  enormous 
quartz  ledges  carrying  gold  in  place  are  in  the  vicinity,  and 
these  have  made  the  placers.  In  another  locality  the  rich- 
est layer  was  the  lower  part  of  the  red  garnet  gravel  resting 
on  the  surface  of  blue  plastic  clay.  Where  the  bed-rock  is 
soft  and  decomposed  it  is  liable  to  be  rich,  but  when  hard 
and  smooth,  poor.  Large  placer  flats  and  elevated  bars 
occur  at  bends  of  the  stream  and  are  rich.  The  region  is 
just  such  as  would  lead  the  prospector  to  expect  rich 
placers.  The  source  of  supply  is  great,  the  side  valleys 
are  excavated  for  miles  along  the  outcrops  of  gold-bearing 
veins,  slates  and  quartzites,  all  contributing  to  the  placer 
of  the  main  valley.  Gold  has  been  partly  retained  in  the 
gulches  and  then  carried  out  and  scattered  far  and  wide  in 
the  drift.  In  flats  and  creek  beds  where  a  stratum  of  soft 
slates  is  found  crossing  the  gulch  below,  a  high  and  hard 
bur  with  rich  deposits  may  be  sought  for.  Pits  were  some- 
times sunk  in  the  flats  near  the  channel  of  the  stream,  but 
failed  to  reach  bed-rock  owing  to  uprising  springs  of  water 
which  could  not  be  controlled.  Panning  has  varied  from  i 
cent  per  pan  to  lo  cents  on  an  average.  On  Bear  Creek 
one  pan  yielded  $27  and  a  rocker  in  8  days  took  up  $165. 
On  Deadwood  Creek  gold  is  derived  from  igneous  rocks 
and  the  gravel  is  of  the  same  material,  yielding  12  colors 
to  the  pan.  Manganese  and  limonite  iron  were  found  asso- 
ciated with  the  gold  san^l,  showing  the  gold  came  from  a 
heavy  manganese  and  iron  ledge  in  the  cliffs.     The  :gold 


240 

i)ein^  cntirel}'  free  from  quartz  appears  to  have  been  de- 
rived directly  from  the  igneous  rock  itself,  not  from  quartz 
veins.  A  j^ravel  wash  from  the  Black  Hills  is  found  all 
!»ver  the  surface  of  the  plains,  made  of  every  kind  of  rock 
found  in  the  hills  and  doubtless  carrying  a  certain  amount 
of  scattered  gold.  Miners  prospecting  up  a  dry  gulch  of 
Whisky  Creek  obtained  25  colors  from  clirt  shaken  from  the 
roo  of  a  small  bush  growing  in  a  crevice  in  the  bare  sand- 
st(.ne  bed-rock  at  the  bottom  of  the  ravine;  hence  the 
locality  is  called  the  Rosebush  diggings,  which  derives  its 
gold  from  the  washing  down  into  ravines,  by  occasional 
heavy  rains,  of  gravel  deposits  capping  the  hills ;  such  a  sud- 
den stream  would  sluice  the  gravel  accumulated  in  the 
gulch,  the  gold  being  cauirht  in  the  crevices  of  bed-rock. 
It  yielded  5  cents  to  15  cents  per  pan.  The  gold  was  in 
fine  panicles  associated  with  gar.i^vs  which  cam.e  from  the 
schists  of  Harney's  Peak.  The  ravine  is  hollowed  out  200 
feet  through  red  sandstones.  Its  bottom  is  paved  with 
Carboniferous  sandstone,  and  the  hills  on  boi'  sides  are 
covered  with  deposits  of  slate  and  quartz  which  furnished 
the  gold.  The  supply  of  water  was  so  small  in  force, 
though  the  deposits  were  rich,  that  miners  v/aited  till 
spring  rains  filled  the  water-holes  and  made  it  possible  to 
work  the  pay  dirt  in  rockers  in  rich  spots.  Most  of  the 
streams  sink  in  their  beds  among  the  foothills  miles  from 
the  ])lacers.  In  dry  ravines  cutting  through  gravel  deposits 
mitiers  can  make  wages  by  washing  the  earth  from  the 
bottom  of  the  gulches  during  early  spring  months  when 
there  is  water  enough." 


PROSPECTING    IN    ARIZONA. 

Arizona  is  in  the  northern  portion  of  the  great  plateau 
system.  We  visited  Prescott  some  time  ago  and  the  mir> 
ing  region  around  the  Hassyampa  Creek.  Between  the 
Union  Pacific  and  Prescott  the  country  is  very  sterile,  com- 
posed mainly  of  contorted  granitic  schists  and  lavas. 
About  Prescott  we  come  into  massive  granite  and  syenitie 
rocks  traversed  by  dark  greenish-gray  dykes  of  diorite. 
These  dykes  are  in  places  gold-bearing,  especially  in  the 
oxidized  decomposed  surface,  yielding  a  good  deal  of  fi,-** 
gold  over  a  considerable  width  of  the  rotten  dyke,  v^hich  at 


241 


le 


the  lime  of  our  visit  was  beinj;  trealc:!  by  an  arastva  iti  the 
creek  below.  At  a  little  depth,  however,  we  found  the  free 
character  of  the  ore  changed  to  rather  rich  K"lU-bcarin^f 
pyrites  requiring  smelting.  On  examining  a  cross  suction 
of  the  dyke,  v/hich  was  upwards  of  loo  feet  wide,  we  found 
it  traversed  by  numerous  little  veinlets,  which  assjiys  showed 
to  carry  the  gold,  the  diorite  matrix  being  p<.or  or  barren. 
The  main  difficulty  in  this  region  is  the  general  lack  or 
uncertainty  of  water,  the  creeks  being  liable  to  dry  tip  at 
certain  seasons  and  to  boom  at  fitful  intervals,  Arizona  is 
noted  also  for  its  rich  copper  mines.  In  the  southern  part 
of  the  State  near  Tombstone  you  rise  from  I'ost-i'lioccne 
gravels  to  a  granite  plateau  of  gray,  crystalline  eruptive 
granite,  weathering  in  gigantic  rounded  blocks  lying  on 
one  another.  Near  Tombstone  stratified  formations  overly 
the  granite,  consisting  of  quartzites,  limestones,  and  slates  of 


:it 


Plate  CVI. 

Arched  Fold,  Toughnut  Mine,  Arizona,  i,  NovacutilH  under  Liini'Hldnt; ; 
2,  Limestone  bending  over  the  Novaculite ;  3,  hhalb.,  bundlnK  uvur  the 
Limestone. 

Lower  Carboniferous  and  of  Paleozoic  age,  dipping  at  a  low 
angle  toward  the  east.  The  Tcughnut  mine,  dcscribud  by 
W.  P.  Blake,  is  an  instructive  one  to  the  prospector. 

"  Here  porphyry  dykes  cut  through  the  strata  following 
the  general  faulting  lines  of  the  country,  the  veins  also 
following  the  same  general  course.  The  stratified  rocks 
are  shales  and  quartzites  very  fine-grained,  the  latter  rock 
changed  to  the  variety  called  'novaculite'  or  whetstone 
rock.  Abundance  of  iron  pyrites  occur  in  the  layers  of 
quartzite.  Above  the  quartzite  are  dark  blue  limestones 
and  black  shales.  The  black  limestones  above  the  novacu- 
lite are  silver-bearing.  These  beds  are  folded  into  arches. 
The  Toughnut  is  on  the  anticlinal  of  one  of  these  arches. 
The  ore  was  discovered  cropping  out  in  the  soil  and  vein 
stuff.  The  rich  ore  lies  in  the  folds.  The  folds  have  also 
27 


242 

broken  into  faults.  The  Grand  Central  Chief  mine  is 
located  in  the  outcrop  of  a  dyke  of  diorile  porphyry  which 
carries  ore,  in,  through  and  alongside  it.  The  prospector 
found  the  outcrop  obscure,  being  a  confused  mixture  of 
porphyry,  flints,  quartz  and  porous  quartzite.  None  of 
the  outcrops  rise  high  above  the  soil.  Ho  was  led,  how- 
ever, to  the  spot  by  a  considerable  stain  of  iron,  and  a  little 
digging  revealed  good  ore  near  the  surface. 

"  The  dyke  varies  in  thickness  from  a  few  feet  to  70 
feet,  dipping  west  55  degrees.  It  cuts  through  the  shales, 
quaitzites  and  limestones.  The  dyke  is  vertically  lami- 
nated or  divided  from  top  to  bottom  by  layers  or  cleavage 
planes  filled  with  thin  veins  of  quartz  (in  this  respect  as 
in  many  others  resembling  the  phonolite  dykes  of  Cripple 
Creek  with  their  cleavage  zones  produced  by  shearing  or 
slight  faulting  movements  and  filled  with  rich  ore).  Large 
portions  of  the  dyke  are  so  penetrated  by  quartz  as  almost 


rata  oouionr 


Plate  CVll. 

Cross  Section  of  the  Mineralized  Dyke,  Contention  Lode,  Arizona.  Show- 
ing %ertical  laminated  structures  with  seams  and  cavities  o£  quartz  crys- 
tals and  ores. 


to  consist  of  that  mineral.  The  dyke  itself  is  much  im- 
pregnated with  pyrites  in  cubes,  many  of  which  having 
dropped  out  leave  square  cavities  and  produce  a  honey- 
combed structure  of  the  quartz.  Though  it  has  been 
worked  600  feet  deep  and  there  are  1 2  miles  of  workings, 
undecomposed  ores  below  water  level  have  not  been 
reached.  The  minerals  are  oxidized  and  so  red  with  iron 
oxide  that  miners  emerge  from  the  mine  like  red  men. 

"  Along  the  upper  300  feet  of  the  dyke  extensive  decom- 
position of  porphyry  has  produced  pure  white  or  stained 
kaolin  or  china  clay.  This  kaolinization  extends  to  the 
adjoining  shales.  The  ores  are  gold  and  silver,  the  gold 
being  free,  the  silver  as  chlorides  with  carbonate  of  lead. 
Metallic  gold  and  silver  chloride  are  disseminated  through 
the  mass  of  the  porphyry,  while  portions  of  the  porphyry 


carry  quartz  veins.     The  porphyry  also  passes  iiUo  soap- 
stone  and  serpentine. 

"  Gold  occurs  in  crystalline  flakes  and  scales  chiefly  in  and 
along  thin  seams  and  cracks  in  the  mass  of  the  rock  as  if 
infiltrated  and  deposited  from  solution.  Free  gold  is  found 
in  the  quartzite.     Both  dyke  and  strata  have  been  moved 


Plate  CVIII. 

Dyke  Matter  Penetrated  by  Veinlets  of  Mineral-Bearing  Quartz. 
Quartz  Veinlets.    Light  Shaded,  Feldspar. 


Biack, 


and  faulted  as  shown  by  breaks  in  continuity  and  by  brec- 
ciated  cross  courses,  seams  traversing  both  igneous  and 
stratified  formations.  This  breaking  up  of  the  dyke  and 
fracturing  and  brecciating  of  the  country  rock,  accompanied 
by  the  movement  of  the  dyke  upon  itself  and  the  formation 
of  heavy  clay  seams,  provided  suitable  places  for  the  accu- 


Plate  CIX. 

Faulting  of  Ore  Body  or  Vein,  Contention  Mine,  Arizona. 


" 


I 


mulation  of  ore  found  in  the  softer,  more  broken  portions 
of  the  dyke.  Bedded  ore  deposits  are  associated  with 
bedded  dykes  and  vertical  fissures  parallel  with  the  Con- 
tention lode.  One  lode  is  traceable  for  two  miles  till  it 
passes  into  underlying  granite. 

"  A  line  of  fissures  cuts  acrops  the  arch  of  the  Toughnut 


244 


m 


which  has  been  followed  in  ore  and  is  connected  with  the 
side  bedded  deposits.  This  lode  is  marked  by  heavy  out- 
crops of  quartz  and  by  flinty  boulders  lying  above  the 
limestone  on  the  surface.  The  bedded  deposits  fill  irregu- 
lar cavernous  spaces  eroded  in  the  strata  by  metalliferous 


Plate  CX. 

Bcdilutl  Deposits  of  Lead  I'assinj?  from  Stratum  to  Stratum,  ll»r<»tiKli  Joint 

Cracks.    (Arizona.) 

solutions  without  definite  boundaries,  and  are  apparently 
explained  by  the  metasomatic  or  substitution  theory. 

"  There  have  been  shearing  movements  of  the  dyke  upon 
itself  resulting  in  heavy  clay  seams  from  attrition,  also 


Plate  CXI. 

Section  of  Moose  Mine  Vein,  Cripple  Creek,  Colorado,  i,  Country  Rock 
breccia ;  2,  Yellow  Jasper  with  Cavities  of  Quartz  Crystals  ;  3,  Blue-gray 
Jasper  with  Seams  of  Quartz  and  Iron  containing  Gold. 


iiiit 


lateral  and  vertical  displacements  from  west  to  east  and 
downward,  the  top  of  the  dyke  having  been  carried  off  in 
successive  blocks  by  the  sliding  of  masses  of  the  stratified 


245 


formations  upon  the  planes  of  deposition  of  the  beds  and 
partly  on  steeper  planes  of  fracture.  These  movements 
have  been  accompanied  favorably  by  ore  occurring  in  the 
softer,  most  broken  portions  of  the  dyke,  coincident  with 
great  original  metallization  and  subsequent  movement  at- 
tended by  clay  seams.  The  fragments  are  not  cemented 
by  quartz  but  loosely  by  clay,  showing  mere  mechanical 
force." 

The  vertical  lamination  of  the  dyke  by  shearing  and  the 
filling  of  the  interstices  so  caused  with  quartz  and  mineral 
is  like  to  what  we  find  so  often  at  Cripple  Creek,  Colorado, 
in  the  mineralized  dykes  of  phonolite  forming  the  lode  of 
many  of  the  mines  such  as  the  Moose,  Elkton,  Raven,  and 
others — phenomena  to  which  the  prospector's  attention  is 
particularly  called,  as  he  is  likely  again  and  again  to  meet 
with  it.     Mr.  Penrose  in  his  description  of  the  veins  of 
Cripple  Creek  gives  a  very  clear  account  of  these  peculiari- 
ties in  ore  deposits.     According  to  him,  "  the  nature  and 
mode  of  occurrence  of  ore  deposits  at  Cripple  Creek  depend 
on  the  character  of  the  fissures  containing 
them.     Fissuring   occurred    before    the 
formation  of  the  dykes  which  filled  the 
fissures.  Sometimes  veins  alone  occupied 
these  early  formed  fissures,  sometimes 
dykes.      Generally,  however,   the  veins 
were  formed  at  a  late  date  long  after  the 
fissuring  and  dyke  filling,  as  the  veins  in- 
tersect the  dykes  following  the  course  of 
pre-existing  fissures  and  intersecting  the 
dykes  longitudinally  or  crossing  them 
diagonally.     There  are  sometimes  two 
systems  of  parallel  fissures.    The  fissures 
are  very  numerous  and  their  course  fol- 
lows that  of  the  veins  and  dykes,  viz., 
northeast    and    northwest  or  generally 
north  and  south.     Fissures  were  not  open  gaps,  but  closed 
lines  of  fracture  and  veins  in  them  are  due  to  replacement 
of  country  rock  along  these  courses.     These  fissures  were 
at  times  held  open  by  loose  fragments  of  rock  broken  from 
the  walls  or  by  protruding  parts  of  the   walls  brought 
opposite   each  other   by  movements   along   the    fissures. 
The  course  of  fissures  is  sometimes  a  clean-cut  break  but 


■rai  mmn>, 


Plate  CXI  I. 

Section  of  the  Zeno- 
bia  Vein,  Cripple 
Creek.  Example  of 
a  clean  cut  fissure 
occupied  bv  a  Brec 
ciated  Vein,  a. 
Vein. 


I>1 

l!H  > 


r46 


ii 

'  5 
»1 


: 


usually  with  parallel  cracks  on  either  side  so  numerous  as 
to  give  the  rock  a  banded,  sheeted  or  slaty  structure,  bome- 
times  not  parallel  but  intersecting,  producing  'linked  fis- 
sures.' Outside  this  fissured  zone  Assuring  becomes  less 
and  less  and  farther  apart  with  receding  from  the  main 


Plate  CXI II. 

Shearing  Parallel  Fissures  Parallel  to  a  Fault. 

Creek. 


C.  O.  D.  Mine,  Cripple 


zone.  This  parallel  fissuring  is  due  to  strong  compressive 
stress  in  which  dislocation  is  spread  over  a  series  of  par- 
allel surfaces  instead  of  confined  to  one  fissure.  The  dis- 
tribution of  these  lines  of  dislocation  in  a  homogeneous 
mass  follows  definite  mathematical  laws.  Fissures  occu- 
pied by  veins  result  from  movement 
and  faulting  as  shown  by  presence  of 
breccia,  groovings  or  striae  and  slick- 
ensides.  These  movements  were  of 
the  nature  of  earthquake  shocks.  The 
character  of  fissures  depends  on  the 
nature  of  the  rocks  they  intersect.  In 
massive  hard  rocks  the  fissures  are 
sharper  than  in  soft  plastic  ones  like 
breccia.  !n  one  case  force  causing  a 
,,    ,.        .  „,, ,      „  .      fissure    overcomes   cohesion    of  hard 

Section  of  Elkton   Vein,  ,  ,  .  ,  i  ,        •        ., 

Cripple  Creek,  .Show-   rock,  makmg  a   sharp  break,  m   the 
ing  reinion  (.f  a  vein   other  only  to  the  extent  of  faint  frac- 

to     sheareu     Phonolite    ,  -^i        .  ^^    ■%    n        ^ 

Dyke.     ^4,  Vein ;  /?,   tures  Without   any    one    well-defined 
Sheared  Dyke;  c,   break.     The  Ore  deposits  are  bodlesof 

Country  Rock.  ,  .  ,    ^i,.        ,,       £. 

secondary  mmerals  fillmg  the  fissures, 
sometimes  a  single  fissure,  sometimes  a  number  of  thin 
parallel  seams  filling  a  fissured  zone.  Ore  deposition  w^as 
a  sequel  to  dyke  action  depending  on  heated  rocks  for  its 
effect.     Dykes  may  liave   cut  water  channels  in  country 


Plate  CXIV. 


■I  ^I't 


I 


247 

rock,  and  water  from  these  channels  forced  up  the  sides  of 
the  dyke  caused  ore  deposition.  Shrinkage  cracks  also  in 
the  dykes  at  their  contacts  with  country  rock  may  have 
offered  favorable  places  for  ore  deposit.  Hence  the  con- 
nection between  veins  and  dykes." 

PROSPECTING    IN    NKW    MEXICO. 

This  is  a  region  characterized  by  great  flows  of  basalt 
and  recent  lavas,  so  recent  that  they  often  cover  the  placer 
grounds  and  modern  river  deposits.  Old  craters  occur  here 
and  there,  and  the  foothills  and  prairie  border  are  studded 
with  lava-capped  mesas.  To  the  west  the  country  is  a  con- 
tinuation of  the  Rocky  Mountain  system,  with  many  rocks 
and  formations  similar  to  those  in  Colorado  and  producing 
much  the  same  ore  deposits  and  in  much  the  same  geolog- 
ical relations.  Thus  there  are  contact  deposits  between 
porphyry  and  Carboniferous  limestones  as  at  Leadville,  and 
fissure  veins  in  granite  as  in  Clear  Creek  County,  Col.,  and 
mineralized  dykes  as  at  Boulder.  The  Rocky  Mountain 
system  is  lower  and  more  broken  up  into  individual  ranges 
than  to  the  north.  Besides  the  veins  of  gold  and  silver  in 
place  there  are  vast  areas  of  gold  placer  ground ;  but  the 
prevailing  feature  is  a  lack  of  water  to  work  them.  The 
great  Rio  Gran-^.e  system,  it  is  true,  traverses  the  region, 
but  the  fall  of  the  river  is  not  sufficient  in  most  part  to 
bring  its  waters  out  of  its  bed  for  mining  operations. 

Lrold  occurs  in  the  Jicarilla  Mountains  but  no  water,  and 
the  gold  ores  in  the  veins  distribute  their  wealth  in  beds  of 
dry  gulches  furrowing  the  sides.  In  Grouse  gulch  a  placer 
occurs  resting  on  hard  red  clay  from  decomposition  of  red 
granite  bed-rock.  At  Santa  Fe  the  gold  placers  lie  in  the 
Placer  Mountains,  for  the  placers  in  this  region  are  true 
"  hill  deposits"  on  slopes  and  ridges  of  the  Rocky  Moun- 
tains carrying  coarse  gold  like  those  of  the  high  plains  of 
California.  Pay  gravel  lies  deep  below  the  surface  and  is 
generally  very  rich.  Absence  of  water  leaves  many  of  these 
untouched.  Mexicans  sink  well-like  shafts,  according  to 
Locke,  through  the  soil  to  the  gravels  and  tunnel  upon 
bed-rock,  and  take  the  richest  gravel  to  the  surface  in 
sacks,  cart  it  two  or  three  miles  to  water,  and  pan  out  the 
gold  in  wooden  bowls  called  "  bateas."  In  winter  they 
obtain  water  by  melting  snow  with  hot  stones. 


34^ 


;*! 


Gold  occurs  locally  in  quart/osc  sandstones  of  Carbonifer- 
ous age  and  in  rusty  beds  rather  than  in  veins.  The  sand- 
stone appears  to  have  been  charged  with  gold-bearing 
pyrites,  by  decomposition  of  which  the  gold  has  been  lib- 
erated. In  localities  there  are  regular  quartz  veins  bearing 
gold  pyrites  which  have  been  worked  for  twenty  years. 
The  erosion  or  breaking  down  of  a  bed  of  sandstone  would 
supply  gold  to  a  stream  or  deposit  without  its  being  accom- 
panied by  beds  of  quartzose  gravel.  So  rich  deposits  may 
exist  on  the  hillsides  without  indications  of  their  presence 
by  beds  of  rolled  gravel  or  broken  fragments  of  veins  on 
the  surface. 

Professor  Silliman,  speaking  of  the  great  placer  deposits 
in  New  Mexico,  says: 

"  Here  are  countless  millions  of  tons  of  rich  gold  quartz 
reduced  by  the  great  forces  of  nature  to  a  condition  ready 
for  the  hydraulic  process,  while  the  entire  bed  of  the  Rio 
Grande  for  40  miles  is  a  sluice  on  the  bars  of  which  the 
gold  derived  from  the  wearing  away  of  the  gravel  banks 
has  been  accumulating  for  coimtless  ages,  and  now  lies 
ready  for  extraction  by  the  most  approved  methods  of  river 
mining.  The  thickness  of  the  Rio  Grande  gravels  exceeds 
often  600  feet,  or  three  times  that  of  the  like  beds  in  Cali- 
fornia, while  the  average  value  per  cubic  yard  is  believed 
to  be  greater  than  in  other  accumulations  yet  discovered." 

The  area,  according  to  him,  covered  by  these  gravels  is 
400  square  miles ;  only  three  portions  of  this  area  are  avail- 
able or  within  reach  of  the  Rio  Grande  waters,  and  the  lava 
circumscribes  much  of  the  river-frontages.  Nothing  corre- 
sponding to  the  "  top  dirt,"  '  pipe-clay"  or  fossil  wood  of 
the  California  gravel  beds  occurs.  The  gravel  for  many 
miles  is  unbroken  except  by  valleys  of  erosion  cut  down 
200  feet  deep  in  them,  with  yet  400  more  before  bed-rock  is 
reached.  The  gravels  above  the  second  "  malpais"  will  be 
of  less  value  than  the  under  bed,  and  zones  of  poor  gravel 
may  occur.  Over  limited  areas  beds  of  fine  yellow  sand 
occur  which  are  poor  or  barren,  but  the  great  mass  of  these 
heavy  beds  are  compact  gold-bearing  gravels  and  contain 
boulders  of  quartzite  with  blue  or  gray  stains  and  seams 
of  magnetic  iron  and  rusty  quartz  stained  by  decomposing 
iron  pyrites,  with  but  few  pebbles  of  granite,  syenite, 
porphyry  or  greenstone  characteristic  of    the  mountain 


249 

ranges,  and  with  no  volcanic  debris  or  ashes.  Quartz  and 
(juartzite  pebbles  form  80  per  cent,  of  the  gravel  in  these 
beds;  the  S(nirceof  the  material  is  from  con r^pondinj;  beds 
of  the  San^re  de  Cristo  Mountains  north  and  cast.  Prospec- 
tors claim  t!iat  the  ^ra\  els  will  average  50  cents  to  75  cents 
to  the  cubic  yard.  An  artesian  well  was  sunk  at  the 
Ranches  de  Taos  423  feet,  and  throu)>j;h  the  entire  depth 
only  gravel  was  met  and  the  material  showed  the  presence 
of  gold  for  the  whole  distance.  Along  the  Rio  (irande 
mining  operations  by  ground  sluicing  have  been  carried  on 
ever  since  this  locality  was  first  possessed  by  the  Spaniards. 
Dredging  is  being  carried  on  in  some  parts  of  the  Rio 
Grande  on  the  bed  of  the  stream  itself. 


CHAPTER   XIX. 


THE      GOLD      OF     THE     ORTIZ      MOUNTAINS     AND 
GALISTEO  AND   RIO   GRANDE   PLACERS.  N.    M. 

Important  mineral  deposits  and  placers  lie  at  the  base 
of  the  Ortiz  Mountains  and  along  the  Galistco  and  Rio 
Grande  rivers.  The  placers  are  being  worked  by  dredges 
by  the  Santa  Fe  Placer  Mining  Company,  to  the  chief  en- 
gineer of  which,  Mr.  F.  E.  Nettleton,  and  to  Prof.  E.  Walters 
(geologist),  we  are  indebted  for  our  information  on  this 
region  as  published  in  the  Southwestern  Manufacturer, 

The  Ortiz  Mountains  are  25  miles  from  Santa  Fe  city. 
The  elevation  of  axis  of  this  mountain  is  10,000  feet  above 
sea  level,  the  valley  of  the  Galisteo  River  at  its  foot  is 
5,674,  at  Los  Cerillos  railroad  station.  Along  this  axis  are 
granite,  syenite  and  porphyry.  East  and  west  of  the  axis, 
paralleling  it,  are  black  trap  rock,  volcanic  dykes  extending 
across  the  country  indefinitely  from  three  to  five  miles  from 
the  axis  of  the  range.  Between  the  axis  and  the  dykes, 
about  three-fourths  of  the  distance,  are  well-defined  lodes 
parallel  to  the  axis  of  the  range.  At  right  angles  to  these 
lodes  are  secondary  lodes  reaching  from  the  primary  down 
to  the  dykes,  especially  on  the  east  side  of  the  range.  The 
great  western  primary  lode  extends  south  to  San  Pedro. 


On  the  secondary  lodes  are  fine  bodies  of  low  grade  ore. 
•^iich  as  Cuiiniiigham  Hill  near  Dolores. 

The  main  western  lode  is  rich  in  copper,  and  copper 
mines,  as  the  San  Pedro  copper  mines.  Others,  such  as  the 
Oipsy  (Juccn  and  "  Lincoln-lucky,"  ari' gold  producers.  The 
nain  primary  lode  on  the  eastern  side  of  the  range  has  been 
worked  at  intervals  since  1711.  soon  after  the  second  con- 
(|uest  of  New  Mexico  by  the  Spaniards.  Senor  Ortiz 
located  on  this  lode  the  celebrated  Ortiz  gold  mines.  The 
vein  matter  of  the  Ortiz  lode  is  decomposed  quartz  carry- 
ing free  gold,  with  depth  changing  to  sulphides  or  pyrites. 
The  Spaniards  worked  out  great  quantities  of  this  ore  by 
means  of  old-fashioned  slopes  and  inclined  galleries,  but 
owing  to  their  crude  methods  they  could  not  successfully 


Plate  CXV. 

The  Ortiz  Mountains  and  Galisteo  River. 


work  the  mines  below  the  depth  that  yielded  the  free  mill- 
ing or*  s. 

The  axis  of  the  Ortiz  Mountain  range  is  in  close  proxim- 
ity to  the  newer  formations  closely  flanking  its  slopes. 
This  uplift  came,  as  in  the  Colorado  range,  after  the  Creta- 
ceous period.  The  axis  is  raised  some  2,000  feet  above 
the  sandstones  flanking  the  mountain,  which  contain  both 
anthracite  and  soft  coal.  The  green  trap-rock  dykes  were 
thrust  up  through  the  newer  formations.  These  Cretaceous 
sandstones  are  soft  and  easily  eroded,  and  form  the  country 
rock  that  tisually  includes  the  gold-bearing  veins,  hence 
a  large  quantity  of  gold  is  freed  and  carried  to  lower  levels 
by  each  rainy  season.  The  slopes  of  these  mountains  are 
so  steep  and  the  sandstone  so  soft,  that  erosion  is  extraor- 
dinarily rapid. 


25" 

On  the  cast  side  the  ratine  are  larRc  liulds  nf  riih  placers 
—deconi  posed  quartz  in  sand  and  K''kVil  w  hi(  h  Ikivl-  inun- 
dated the  entire  eastern  shtjie.  Here  are  millions  of  cubic 
yards  of  j^old-bearinj;  material  resting?  on  soft  samlstone. 
These  deposits  were  made  in  a  past  a^c  after  the  mountains 
uplifted  and  had  atTorded  great  (luantities  of  ^old-hearing 
material  freed  by  the  rauid  erosion  of  the  coinitry  mck. 
Above  the  main  eastern  ayko  and  paralleling  it  for  several 
miles  is  probably  the  richest  "dry  placer"  in  the  entire 
field.  The  geology  of  the  region  is  simple  :  the  strata  rise 
from  the  (ialisteo  River  at  an  angle  of  lo  degrees  up  to 
the  primary  main  eastern  lode.  Hetween  that  and  the  a.xis 
of  the  mountain  the  incline  is  much  greater.  The  lode  is 
in  a  true  fissure  into  which  the  vein  material  has  been  in- 
jected. 

The  sandstone  constituting  the  general  matrix  of  the 
country  rock  is  so  soft  and  porous  that  the  vein  matter  lying 
near  the  surface  rapidly  oxidizes.  The  oxidized  honey- 
combed quartz  remains,  with  its  vast  supply  of  free  gold  that 
erosion  is  gradually  freeing  and  carrynig  down  the  slopes 
to  feed  the  placers  below. 

The  great  trough  that  affords  a  line  of  rest  for  these 
enormous  placer  deposits  is  the  bed  of  the  Galisteo  River. 
This  river  is  four  to  ten  miles  from  the  main  eastern  lode, 
and  close  to  the  dry  placers  which  are  from  hundreds  to 
thousands  of  leet  higher  than  the  river,  though  the  deposit 
extends  in  more  or  less  richness  down  to  the  banks  of  the 
river.  There  is  considerable  uniformity  of  values  through- 
out the  field.  Placers  of  workable  richness  are  found 
almost  anywhere  where  there  are  drift  deposits  on  tlie 
entire  eastern  slope  of  the  range. 

Water  supply  is  the  most  difficult  problem.  The  Cun- 
ningham mesa,  or  "  old  placers,"  on  the  eastern  slope  has 
been  worked  for  hundreds  of  years  by  ancient  Aztecs  and 
later  Spaniards,  yet  it  is  said  by  experts  that  if  water  could 
be  brought  to  bear  the  placers  could  yield  a  million  annu- 
ally for  twenty-three  years  despite  the  hundreds  of  past 
years  they  have  been  worked.  These  dry  placers  have 
only  been  worked  hitherto  by  the  Mexican  dry  washer  and 
by  "  batea"  and  dry  panning  and  hauling  the  material  to 
the  nearest  water  on  the  backs  of  burros.  Hundreds  of 
thousands  of  dollars'  worth  of  gold  have  l)een  extracted,  and 


3<;2 


i 
'I 


Still  but  a  minntc  fraction  of  the  deposit  has  tjeon  touched. 
For  live  miles  frotn  I^os  Cerillos  to  Ortiz  station  he  bed  of 
the  Galisteo  River  is  a  rich  placer  and  will  pan  well  where- 
ever  samples  are  taken.  The  sandstone  bed-rock  is  1 5  to 
35  feet  below  the  surface.  There  is  not  enough  fall  and 
pressure  power  in  the  river  for  hydraulicking  the  dry 
placer  above.  The  next  nearest  is  the  Rio  Grande.  The 
water  in  the  river  is  mostly  "  sub-flow"  penetrating  the 
deposit  from  top  to  bottom,  hence  all  the  material  is  in  a 


/tssuv     I 'a /lie] 
pi-r  Ch.  Yd. 

10  cts.. 


$2.75.. 

3-75- 

4.0J.. 

<,.40 

4.94. 


•  %«•—••••• 


\: :: —  •.•.••.••••■-" 


f).  25 .  • . . 


.River  bank,  lo  feet. 


.Coarse  drift  sand,  3  feet. 


.Adobe  clay,  3  feet, 
.('oarse  gravel,  i  foot. 
.Adobe  clay,  i  foot. 

Coarse  sand  and  gra%'el,  4  feet. 

.Gravel  and  stones,  2  feet. 
.Fine  sand,  2  feet. 

.Large  gravel  and  stones,  4  feet. 

.Coar.se  sand,    gravel   and  stones 
3  feet. 

.Gray    sandstone,  dipping  20°   1". 
(bed-rock). 


MHO  MmTAL  MiMmm. 

Plate  CXVI. 

Section  of  Rio  Grande  Rivtr  Med,  showing  Strata  Values. 

partial  state  of  suspension,  so  that  any  particle  of  gold  lodg- 
ing on  the  surface  finds  its  way  to  the  bottom,  where  it 
remains.  Thus  the  material  near  the  surface  shows  $2.46 
and  at  bed-rock  $6.42  per  cubic  yard. 

The  Santa  Fe  Placer  Company  used  the  air  caisson  for 
maUine  tests  of  the  materials,  the  strong  sub-flow  prohibit- 
ing the  use  of  the  (irdinary  cut  and  pumps.  The  stratifica- 
tion of  the  matter  penetrated  is  shown  in  the  sketch. 


253 


MoHK.    or    WORKINc;    IT  ACF.R. 


The  process  proposed  for  extractinjj  the  gold  is  i)y 
the  Nettleton  placer  raachine.  a  powerful  steam  bucket 
dredge  of  a  capacity  of  i  cubic  yard  <^f  inatt-rial  per  iniii- 
ute,  having  as  an  auxiliary  a  six-inch  ^t'ntrifngal  pump, 
whose  suction  pipe  will  extend  down  tip  Iredge  ladder  to 
within  1 2  inches  of  the  lowest  i:>oint  reached  by  the  buckets. 
This  pump  will  not  only  bring  up  the  neces«»try  water 
for  sluicing,  but  such  loose  material  as  mav  be  left  by  the 
buckets  and  in  a  great  measure  clear  the  bed-'ock  of  gold. 
The  product  of  dredge  and  pump  is  deposited  in  a  sluice 


Plate  CXVII. 

The  Nettleton  Placer  Mining  Machine  for  River  Work, 

Yards  per  Day. 


Capacity,  low 


box  25  feet  above  the  deck  of  the  barge,  from  which  eleva- 
tion the  work  is  done  by  gravity  until  the  material  and 
water  is  disposed  of.  Passing  down  the  first  sluice  of  30 
feet  a  grizzly  or  grating  is  reached,  removing  stones  over 
3  inches  in  diaineter,  finer  material  passing  through  screens 
which  reduce  it  to  one-half  inch.  So  the  non-productive  ma- 
terial is  removed  at  once  and  deposited  behind  the  barge. 

Having  passed  through  the  screens,  the  material  and 
water  fall  into  a  box  containing  quicksilver  and  thence 
flow  into  table  sluices,  giving  additional  length  of  sluice  of 
70  feet,  by  which  time  even  the  freest  gold  has  gravitated 
in  the  riffles  of  the  sluices  and  been  held  there  by  quick- 
silver, with  which  they  will  be  charged.     The  percentage 


254 


i 


of  fine  flour  gold  being  very  large,  tbe  material  is  passed 
over  a  burlap  sluice,  the  fibers  of  vvhicli  arrest  and  hold  the 
gold.  Tile  usual  accompanying  "  black"  or  magnetic  iron 
■  sand"  carries  a  great  dt;al  of  goUl,  as  high,  so  it  is  reported 
at  times,  as  $2,000  per  ton,  the  gold  probably  in  sulphides. 
To  save  this,  after  pissing  the  burlap,  the  luatter  comes  in 
contact  with  strong  magnets  placed  in  the  circumference  of 
a  cylinder,  the  iron  adhering  to  the  magnets,  from  which  it 
is  removed  b_,  a  revolving  brush,  the  non-magnetic  matter 
passing  on  to  a  revolving  screen,  where  it  is  reduced  to 
one-sixteenth  inch  preparatory  to  being  run  over  amal- 
gam plates,  such  as  are  used  in  stamp  mills,  or  into  a  series 
of  boxes  filled  with  quicksilver.  By  this  time  all  collecta- 
ble gold  will  have  been  saved,  and  after  being  run  through 
traps  to  save  any  strav  amalgam  or  quicksilver  the  now 
unproductive  material  will  pass  into  a  tailings  well  and  be 
taken  up  by  an  8-inch  centrifugal  pump  and  depositf^d  far 
beh'nd  the  boat.  Fine  sand  settling  in  the  riffles  of  the 
c'iuices  or  burlap  will  be  treated  with  cyanide.  Depressions 
in  bed-rock  the  dredge  cannot  reach  v/ill  be  reached  by  the 
air  caisson  and  bed-rock  thoroughly  cleaned. 

Another  plan  suggested  is  to  raise  the  material  andw^ter 
for  sluicing  with  a  centrifugal  pump  to  the  amalgamating 
plant  placed  on  the  bank.  Large  stones  and  gravel  from 
the  screens  will  be  deposited  in  the  excavation  back  of  the 
workings  and  the  fine  tailings,  sluice  and  surplus  water 
will  be  conducted  down  the  river  by  flume  a  sufficient  dis- 
tance to  prevent  its  return.  This  plan  will  enable  the  bed- 
rock depressions  and  crevices  to  be  cleaned  by  hand  at  less 
expense  than  by  dredge  or  caissons.  The  waier  flow  of  the 
river  will  not  exceed  10,000  gallons  per  minute  during  10 
months  of  the  year.  So  no  great  capacity  of  pumps  will 
be  needed.  The  natural  conditions  have  made  the  Galisteo 
River  a  promising  placer  proposition.  The  extent  of  its 
gold  deposits  can  only  be  conjectured. 


'■i  U 


255 


CHAPTER    XX. 


THE    GOLD 


AND     SILVER    ORE    DEPOSITS    OF 
MERCLR   DISTRICT.  UTAH. 


THE 


For  our  information  on  this  district  wu  art-  indebted  to 
the  valuable  reports  of  the  United  States  Oculo^ical  Survey 
by  Mr.  S.  F,  Emmons  and  Mr.  E.  Spurr.  From  the  base  of 
the  Wahsatch  Mountains  on  the  east  to  the  Sierra  Nevada 
on  the  west  is  an  arid  region  called  the  (ireut  Basin,  be- 


Plate  CXVIIX. 

Mercur  Basin,  Looking  South,  Meruur  Hill  on  lliu  UIkIiI, 

cause  it  has  no  sxternal  drainage  to  the  ocean.  This  was 
once  occupied  by  two  large  fresh-water  seas,  represented 
now  by  only  small  salt  lakes.  The  Basin  consists  of  broad 
level  valleys  6,000  feet  above  the  sea,  intersected  Ijy  moun- 
tain ridges  called  the  Basin  ranges.  The  Oquirrh  range, 
in  which  is  the  Mercur  gold-mining  district,  is  the  first  of 
these  ranges  west  of  the  Wahsatch,  about  13  miles  from 
them.  The  Great  Basin  is  an  arid,  .sage-brush  desert.  A 
few  small  streams  arc  in  the  Oquirrh  range  but  insufficient 


I  i 


256 

for  mininjijpnrpo.-^cs.  The  raiiKc  is  jomilcs  lonjj,  cultninal- 
iiij;  in  Lewiston  I\'ak,  10,628  feet  above  the  sea. 

Utah  has  hitherto  been  celebrated  more  for  its  silver  than 
.i;()ld  products.  Hence  the  importance  of  the  gold-mining 
district  of  Mcrcur. 

Hi.igham  Canyon,  Ophir,  Stockton,  Camp  Floyd  and 
Tintic  liave  all  been  noted  more  for  their  silver  than  for 
i;i)ld.  The  Oquirrh  Mountains  are  composed  of  Carbonif- 
erous limestones  and  quartzites  compressed  into  a  series  of 
complicated  folds,  accompanied  by  metamorphism  and  in- 


Plate  CXIX. 

Mcrcur  Basin,  Looking  Nortli,  Nfarion  Hill  in  Left  Foreground. 

jection  of  porphyry  sheets  and  dykes  with  subsequent  min- 
eralization in  the  more  disturbed  districts.  The  Lower  Car- 
boniferous limestone  of  Lewiston  canyon  is  the  ore-bearing 
horizon  of  the  Mercur  district.  On  the  north  side  of  Ophir 
canyon  an  arch  of  Cambrian  quartzite  has  been  uplifted  by 
a  fault.  There  are  no  large  exposures  of  eru])tiv'e  rocks 
such  as  result  from  eruptive  overflows,  but  rather  narrow 
dykes  and  intrusive  sheets.  In  Bingham  Ce.nyon  the  ore 
occurs  only  in  the  vicinity  of  porphyry  bodies  that  occur 
there.  In  the  Mercur  district  the  igneous  rocks  are  in  thin 
sheets  parallel  to  the  stratification,  and  beneath  these 
sheets  the  ore  deposits  occur.  There  have  been  two  dis- 
tinct periods  of  mineralization.  During  the  first  the  silver 
lodge  was  formed,  during  the  second  the  minerals  of  the 
gold  ledge  were  deposited.     In  both  cases  the  ore  was  de- 


257 


posited  alonjjf  the  lower  contact  of  a  ])orpliyry  sheet  where 
a  porous  or  brecciated  /one  has  been  formed  l)y  intrusions 
of  igneous  rock  which  the  mineralizing  solutions  reached 
through  fractures  or  fissures  extending  downwards  from  the 
respective  sheets.  The  principal  vein  materials  of  the 
sliver  ledge  are  silica,  barium,  antimony,  copper  and  silver 
brought  up  by  ascending  hot  solutions  as  sulphides  and 
sulphates.  They  were  deposited  in  the  contact  zone  below 
the  lowest  porphyry  sheet  and  occasionally  above  it.  The 
limestone  in  this  zone  is  replaced  by  silica.  The  fissures 
through  which  the  mineral  solutions  ascended  have  since 
been  filled  with  calcite. 

There  are  two  kinds  of  quartz  porphyry.  The  Eagle 
Hill  porphyry  is  a  light  white  rock,  like  Leadville  white 
porphyry;  the  Birdseye  is  gray  and  speckled  with  horn- 
blende mica  quartz  and  feldspar  crystals.  Two  ore-bearing 
beds  or  zones  loo  feet  apart  occur  near  the  middle  of  a 
great  series  of  limestones.  The  lower  bed  is  of  a  dark 
silicified  quartzose  limestone,  brecciated  and  porous,  carry- 
ing silver,  copper,  antimony,  but  no  gold.  It  is  called  the 
Silver  ledge.  The  upper  zone,  called  the  Gold  ledge,  is  of 
decomposed  bleached  red  or  yellow  limestone  and  shale 
containing  realgar  and  cinnabar  'vith  low  but  uniform  per- 
centage of  gold. 

The  Silver  ledge,  owing  to  the  hardness  of  the  rock, 
causes  it  to  stand  out  as  a  distinct  ledge  and  is  easily  fol- 
lowed, but  the  Gold  ledge  of  softer  material  could  only  be 
traced  by  a  slight  ochreous  appearance  in  the  rock.  The 
gold  is  invisible.  Certain  beds  supposed  to  be  clay  or  shale 
in  the  mine  proved  to  be  altered  sheets  of  white  porphyry. 
Three  cl  these  were  traced  on  the  ore-bearing  zone  and 
revealed  the  oft-observed  connection  of  igneous  rock  and 
ore  deposit.  Th^  vein  materials  of  the  gold  ledge  are 
realgar  (sulphide  of  arsenic),  cinnabar,  pyrite  and  gold, 
with  these  are  barite,  calcite  and  gysum.  The  deposits 
occur  at  thr  intersection  of  zones  of  fracture  with  the  lower 
contact  of  the  middle  of  the  three  porphyry  sheets,  reaching 
a  thickness  of  20  feet.  Some  of  the  fissures  are  still  open, 
showing  no  evidence  of  filling  or  erosion  by  circulating 
waters.  (See  Plate  CXX. )  These  fractures  cut  across  the 
silver  ledge  and,  as  a  rule,  do  not  extend  above  the  gold 
ledge. 


^i. 


25« 


W 


The  section  of  the  region  is  as  follows 

1.  Blue  gray,  Lower  Carboniferous  limestone  occupying 
the  bottom  of  the  canyons,  200  feet  thick. 

2.  Interbedded  limestones  or  calcareous  sandstones,  600 
feet. 

3.  Thick  blue  gray  limestone,  5,000  feet  thick,  cf)ntaining 


J    'V'  .      , 

Plate  CXX. 

Natural  Open  Fissures  in  the  Face  of  the  LJiift  of  ihe  Silver  Cloud  Mine, 

in  Silver  Ledge,  Mercur. 

thin  Strata  of  water-bearing  shale,  and  in  its  lower  portion 
it  carries  the  ore  horizons. 

4.  Above  this  again  more  lunestoiies  and  sandstones, 
5,000  feet  thick.  So  in  Mercur  Basin  a  total  thickness  of 
12,000  feet  of  strata  is  exposed. 


259 


As  the  hills  around  Mercur  are  not  covered  by  drift  it  is 
easy  for  the  prospector  to  trace  the  line  of  contact  between 
the    eruptive   porphyries    and    sedimentary   rocks.      The 


c  EP 


«Mo  UKrsL  Mtmmm- 
BP 


Plate  CXXI. 


Map  and  Section  of  the  Oquirrh  Mountains.  D,  Drift ;  7,  C\  Lower  Cs 
niferous;  (/  C,  Upper  Carboniferous  ;  C,  Cambrian  ;  £  J',  Bagle  Hill 
phyry  ;  B  /*,  Birdseye  Porphyry. 


Carbo- 
Por- 


zone  can  generally  be  identified  by  fragments  lying  on  the 
surface.  In  the  weathered  rock  limestone  chips  are  of  the 
typical  dark-blue  color,  while  those  of  porphyry  are  yel- 


26o 


I 


■i^ 


I   ' 


low,  browti  or  jj;rccti.  On  a  bare  hillside  the  line  separat- 
inj^  the  two  can  ha  easily  traced.  The  Birdseye  porphyry 
weathers  an  olive-^rcen  colrr  and  the  Ea^le  porphyry  gen- 
erally breaks  up  into  small  blocks  and  chips. 

Most  of  the  rocks  in  the  Mercur  Uasin  showtracesof  gold 
like  at  Cripple  Creek.  Col.,  suggesting  a  widespread  miner- 
alization. The  porphyries  showed  the  highest  traces  and 
the  limestones  the  least.  Pure  white  calcite  veins  uncon- 
nected with  the  main  mineralization  showed  small  quan- 
tities of  gold.  Certain  localities  are  so  greatly  mineralized 
as  to  furnish  profitably  worked  bodies  of  gold  and  silver 


'C 


V  ra  MP  Mar***  l<M  <i 
j  On  14  l^*f 

U'nr.lfit  ' 


l^rphyry  Vltne»tvn« 

mninj      prrn 

Plate  CXXII. 

Ueulugical  Section  of  Mercur  basin. 

ore.  These  localities  are  at  the  contact  of  porphyry  sheets 
with  enclosing  limestone.  In  localities  only  is  this  contact 
line  rich.  In  one  group  the  limestone  is  hardened  at  con- 
tact with  the  porphyry  into  what  miners  call  "  black  quartz" 
showing  silver  chloride,  antimony,  copper  carbonate  and 
barite.  In  the  other  groups  limestone  and  porphyry  are 
decomposed  into  a  soft  black  shaley  substance.  The  first 
group  contains  silver,  the  second  only  gold  together  with 
arsenic  and  cinnabar.  The  one  is  the  silver,  the  other  the 
gold  ledge.  The  rock  forming  the  contact  of  the  silver 
ledge  is  much  broken  or  brecciated,  the  fragments  com- 
posed of  cherts  and  silicified  limestone  inclosed  in  cement 
of  white  calcspar  and  barite.  The  greater  erosion  of  the 
softer  porphyry  leaves  a  distinct  shelf  or  ledge  20  feet 
wide. 


Ut 


In  the  limestone  below  the  ledge  are  many  vertical  cal- 
cite  veins  formed  by  the  intrusive  action  of  the  porphyry, 
as  was  also  the  breccia  or  broken  element  in  the  ledge,  and 
the  interstices  were  healed  by  solutions  of  calcite.  Hard- 
ening and  darkening  of  the  limestone  are  noticeable  at  this 
tipper  contact  for  3  feet.  Three  sheets  of  porphyry  are 
developed  on  the  hill,  one  20  feet  thick  associated  with 
the  silver  ledge,  and  the  lowest,  above  this  a  smaller  sheet, 
much  decomposed,  associated  with  the  gold  ledge,  and 
above  this  a  third  unmineralized.  At  the  bottom  of  the 
Silver  Cloud  mine  are  many  open  fractures  without  vein 
filling,  indicating  the  action  of  faulting.  They  were  later 
than  the  vein  filling  of  the  silver  ledge.  Large  geode  cav- 
ities lined  with  calcspar  crystals  occur  in  the  vein,  together 
with  a  network  of  calcite  veins;  bunches  of  barite,  stains 
of  green  malachite,  and  azurite  copper  occur,  and  a  good 
deal  of  kaolin  in  crevices.  The  open  fissures  show  their 
later  origin  by  cutting  through  all  these.  The  softer  and 
decomposed  porphyry  is  actively  prospected  for  gold. 

A  black,  flinty  impure  quartz  accompanies  the  ore. 
Changing  of  the  limestone  into  a  quartz-like  condition  was 
one  of  the  first  stages  of  metamorphic  action.  The  quartz 
is  generally  this  "  horn"  or  flinty  amorphous  ^aartz.  Crys- 
tals are  rare.  The  latter  occur  in  irroi^ular  cracks  and  cavi- 
ties produced  by  solutions.  Th\  honeycombed  nature  of 
the  rock  is  what  mainly  shows  the  intensity  of  the  action 
accompanying  mineralization.  The  calcite  veins  are  gen- 
erally barren.  Barite  or  hea\-\  spar  is  closely  associated 
with  the  ores  occupying  Itregular  spaces  in  the  rocks  and 
is  a  sure  sign  of  con^Jiderabie  mineralization.  Barite  often 
forms  the  gangue  in  Which  the  ore  is  imbedded.  Antimony 
occurs  in  radiating  crystals  and  bunches.  Copper  stains 
are  associated  with  the  silver.  "  Chinese  talc"  or  gouge,  a 
clay  resulting  from  decomposition  of  *he  porphyry,  occurs 
as  at  Leadville.  The  silver  (»re  consists  ot  small  films  of 
chloride  of  silver  disseminated  through  altered  silicified 
limestone. 

Mineralization  has  taken  place  at  the  con  act  of  porphyry 
and  limestone.  From  this  it  extends  into  the  limestone 
away  from  the  porphyry,  mineralizati</ft  decreaning  in  force 
as  it  recedes  from  the  line  of  oonfart  ^8ee  Plates  (XXI 11 
and  CXXIV.)     The  mineralizing  agents  were  heated  waters. 


362 


circulating  alonjf  the  contact,  containing  silica,  barium,  an- 
timony, copjKT  and  silver.  The  work  of  these  solutions 
was  the  leaching  out  and  removal  of  lime  and  replacement 
of  it  by  silica  without  destroying  the  original  features  of 
the  rock.     Quartz  in  the  vicinity  of  eruptive  rocks  is  apt  to 


B3 

Limes  font'. 


Silver  Ledge 

mm 


[O 


/'orfifiyrv.     (iolJ  heiiriiif;  ore.     Wrtical fissures. 
Pl.ATK    C'XXII'. 


fleolojfical  Seotiuii  of  I'ait  of  llie  Meiiur  Mine. 

accumulate  in  compact  crystalline  masses  or  in  a  fiint-like 
jaspery  or  chalcedonic  condition,  and  the  silicifying  of  the 
limestone  at  contact  with  porphyry  at  Mercur  is  only  a  nat- 
ural and  common  result  of  metamorphic  action. 

Limestone 

Porphyry 

Ore 

Limestone. . . 


rw*  «Q(ju««r  CNMi««wi  mio  mmink.  mmum- 


Plate  CXXIV. 

Section  ulon^  Geyser  Tunnel,  Mercur. 

Water  contained  in  lavas  is  not  given  oil  till  just  at  the 
moment  of  solidification  of  the  lava,  when  it  is  separated 
out  and  apppears  as  a  fluid.  When  this  solidification  takes 
place  at  the  surface  it  forms  clouds  of  steam  so  generally 
visible  on  cooling  lavas,  but  v;hen  the  lava  is  forced  in,  in  a 
molten  state  underground,  between  strata  the  water  is  still 
under  sufficient  pressure  to  keep  it  in  a  liquid  state.     From 


2(>i 


this  result,  intensely  la.iled  solutions  arise  capable  of  mueh 
corrosive  elTect  on  the  rocks  and  of  aidinj;  ore  solution. 
These  solutions  act  most  violently  at  the  contact  and  be- 
come rapidly  cooled  on  penetiatiujj;  the  adjoining;  rock. 

The  plicUMinena  at  the  silver  ledj;e  indicate  brief  intense 
action,  lii>;lily  heated  waters  with  ^reat  luetamorphosinK 
and  corr  linj;  power.  The  mass  is  full  of  cavities  showing 
this.  Tlie  l)ariinn  found  in  the  silver  ledj^e  was  derived 
frotn  the  porphyry,  as  probably  were  the  metals,  which  were 
deposited  as  at  Steamboat  Springs,  Nev.,  by  ascending  hot 
solutions.  These  exuding  at  every  point  in  the  cooling 
porphyry  found  in  the  limestone  a  zone  where  the  passage 
of  sohitions  was  easy  by  opening  of  Hssutes  and  formation 
of  breccias.  The  heated  waters  under  great  pressure  would 
move  along  this  broken  weak  zone,  as  also  occasionally  in 
an  upward  direction.  Where  porphyry  sheets  cut  across 
the  strata  water  would  rise  rapidly.  Where  circulation 
was  retarded  accumulation  and  mineralization  would  be 
greatest.  In  the  case  of  the  gold  ledge  the  mineralizing 
agents  were  probably  more  in  a  gaseous  than  a  liquid  con- 
dition. The  various  metals,  antimony,  cinnabar,  etc., 
found  associated  with  the  gold  are  such  as  would  easily 
pass  into  the  state  of  vapor  and  be  the  last  deposited. 
After  the  eruption  of  the  porphyry  a  disturbance  brought 
about  a  set  of  vertical  fissures  establishing  a  communica- 
tion with  a  body  of  uncooled  igneous  rock  at  an  uncertain 
depth,  affording  a  vent  for  moist  volcanic  vapors,  and  along 
the  porous  zone  at  contact  of  porphyry  and  limestone,  and 
in  the  brecciated  limestone  the  vapors  spread  out  and  be- 
coming cooled  deposited  the  gold  and  associate  minerals. 

The  gold  .  dge  is  a  mineralized  zone  in  the  lower  part  of 
Mercur  Basil.  It  consists  of  an  altered  limestone  follow- 
ing the  under  contact  of  a  thin  sheet  of  altered  porphyry. 
The  thickness  of  the  contact  zone  varies  from  20  feet 
down  to  nothing.  The  lines  of  greatest  mineralization 
coincide  in  direction  with  p.  Ect  of  vertical  fissures  forming 
shoots  or  channels. 

The  ores  are  oxidized  or  else  sulphides.  The  former  are 
extracted  by  the  cyanide  process,  the  latter  by  roasting. 
The  zone  is  soft  and  pulverulent  and  full  of  cherts.  The 
amount  of  gold  in  the  ores  rarely  exceeds  3  ounces  to  the 
ton.     Silver  is  absent. 


.^J^ 


IMAGE  EVALUATION 
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Photographic 
.Sciences 
Corporation 


23  WEST  MAIN  STREET 

WEBSTER,  N.Y.  14SS0 

(716)  172-4503 


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CHAPTER  XXI. 


SALTING  MINES. 


In  these  days  when,  owing  to  the  depression  of  silver,  so 
much  attention  is  being  turned  towards  gold  and  gold 
mines,  too  much  care  cannot  be  taken  by  those  investing 
or  acting  as  examiners  or  experts  in  gold  mines,  that  there 
are  no  tricks  played  upon  them  by  the  astute  miner ;  for 
"  for  ways  that  are  dark  and  tricks  that  are  vain"  the 
Western  miner  is  at  times  "  peculiar."  One  of  these  tricks 
is  what  is  known  as  "  salting"  mines  or  ledges ;  that  is,  by 
various  means  and  ways  introducing  into  the  mine  or  into 
the  samples  taken  from  it,  certain  rich  minerals  which  do 
not  rightly  belong  by  nature  in  the  mine  or  property,  in 
order  to  raise  the  value  of  the  mine  in  the  eyes  of  the  in- 
vestor or  expert.  When  samples  are  taken  from  such  a 
tampered-with  mine  the  values  and  results  must  be  ac- 
cepted cum  grano  salts,  with  a  very  large  grain  of  salt  in- 
deed. Whether  this  classical  allusion  be  the  origin  of  the 
word  "  salting"  we  do  not  know. 

"  Take  care  you  ain't  salted"  is  the  advice  to  the  inex- 
perienced investor  or  novice  expert.  So  clever  are  the 
miners,  that  cases  are  on  record  where  even  a  most  experi- 
enced expert  has  been  taken  in,  and  comparatively  or 
wholly  valueless  properties  sold  for  large  sums,  the  pur- 
chase followed  later  by  woful  dismay  and  surprise,  when 
dividends  were  called  for  and  did  not  appear. 

Gold  mines,  of  all  others,  are  the  most  easy  to  salt,  hence 
the  precaution  in  these  days  is  timely. 

Whilst  a  mining  engineer  or  expert  can  hardly  prevent 
salting,  with  care  he  can  and  ought  to  be  able  to  avoid  be- 
ing taken  in ;  to  be  forewarned  is  to  be  forearmed. 

On  entering  a  mining  camp  in  the  far  West,  especially  in 
the  more  remote  outlandish  districts,  an  investor  or  an  ex- 
pert may  consider  that  the  whole  village,  from  the  hotel 
bell-boy  to  the  mayor  (who,  by  the  way,  may  be  the  prin- 
cipal saloon-keeper),  is  in  league  against  him.  Directly  he 
arrives,  everybody  in  town  wants  to  know  his  business ;  on 


// 


265 

this  he  should  keep  as  mum  as  possible,  and,  if  he  can, 
throw  impertinent  inquirers  off  the  scent.  The  idea  is, 
"  Here  is  a  capitalist  to  fleece  and  an  expert  to  delude." 
Every  one,  too,  has  a  "  hole  in  the  ground"  of  his  own  to 
present.  Should  they  get  wind  of  the  particular  property 
in  view,  there  are  confederates  and  middlemen  anxious  to 
share  the  spoils.  Moreover,  it  is  considered  to  the  general 
credit  of  the  camp  to  sell  a  mine,  be  it  whose  it  may,  good 
or  bad,  and  if  you  mention  any  property,  you  will  invari- 
ably hear  it  "xiracked  up."  The  Eastern  "  tenderfoot"  is 
somewhat  of  a  "sheep  among  wolves"  in  such  a  camp. 
The  expert,  too,  is  at  a  certain  disadvantage  on  entering 
into  a  strange  mining  camp,  not  being  familiar  with  the 
local  conditions.  Ores,  for  instance,  in  one  section  or  re- 
gion are  not  always  of  the  same  value  as  similar  ores  in 
another,  the  rocks  may  look  new  and  strange  to  him,  and 
there  are  a  hundred  local  conditions  known  only  to  the 
resident  miner.  It  would  be  well,  when  poss'ble,  for  an 
expert,  before  passing  a  decided  opinion  on  an  important 
property,  to  stay  around  in  the  vicinity  for  a  while  till  he 
knows  the  "  hang  of  things." 

On  his  way  to  the  mine  there  will  be  plenty  to  fill  his 
ears  with  the  untold  value  of  the  property  he  is  about  to 
examine ;  this  friendly  duty  is  not  unfrequently  performed 
by  an  officious  middleman.  To  favor  and  "  soften  up"  the 
expert's  mind  and  heart  and  make  him  "  feel  good"  toward 
the  property,  attentions  of  all  kinds  are  showered  on  him. 
He  is  driven  about  town  like  a  nabob,  and  if  he  shows  a 
weakness  for  a  "  wee  drappie,"  champagne  and  whiskey  are 
at  his  service  ad  lib. ,  as  judicious  preparation  for  the  com- 
ing examination.  It  may  be  observed  here  that  attempts 
are  made  sometimes  to  "salt"  the  expert  as  well  as  the 
mine,  not  merely  by  befuddling  his  brain  with  intoxicants, 
but  by  offering  bribes,  and  as  an  expert  is  often  not  too 
well  off,  the  latter  is  a  great  temptation. 

We  will  now  suppose,  after  this  ordeal,  he  goes  to  the 
mine  with  the  superintendent  or  miner.  All  may  be,  and 
we  may  say  generally  is,  honest  and  square,  or  it  may  not. 
The  expert  looks  over  the  exterior  and  surface  signs  of  the 
property,  studies  the  outcrop  of  the  vein  on  the  surface,  its 
probable  surface  continuity,  the  advantages  and  disadvan- 
tages of  the  situation  of  the  mjne,  its  proximity  to  rail- 


266 


roads,  smelting  works,  markets,  etc.,  and  then  enters  the 
mine  in  company  with  the  miner.  As  a  rule  the  latter  will 
naturally  point  out  lo  him  the  richest  portions  and  ignore 
the  poorer ;  sometimes  he  excuses  himself  from  taking  him 
down  into  the  latter  because  it  is  dangerous  or  full  of  water. 
If  full  of  water  the  expert  if  possible  should  have  it  pumped 
out.  He  may  suggest,  here  and  there,  that  such  and  such 
a  spot  would  be  a  good  one  for  the  expert  to  take  his  sam- 
ples, and  so  forth.  The  expert  of  course  assents  to  all  he 
is  told,  but  with  one  eye  open,  and  does  not  stop  to  take 
any  samples  for  assaying  until  he  has  seen  the  whole  of  the 
mine;  then  he  requests  his  companion  to  go  out  on  the 
dump  and  smoke  his  pipe  there,  as  he  insists  upon  having 
no  one  with  him  in  the  tunnel  when  he  is  taking  his  sam- 
ples for  assay.  He  will  be  inclined  to  rather  avoid  those 
particularly  favorable  spots  suggested  to  him  by  the  miner, 
as  probably  giving  too  rich  an  average  for  the  general  run 
of  the  mine,  or  as  not  impossibly  being  "  fixed"  for  him.  If 
he  suspects  the  latter,  he  will  take  a  sample  or  two  to  see 
if  the  mine  has  been  tampered  with,  taking  a  little  of  this 
out  on  the  dump,  crushing  it,  and  washing  it  in  an  iron 
spoon.  If  a  very  astonishing  amount  of  gold  colors  show 
up,  his  suspicions  are  aroused.  The  judicious  miner  does 
not  generally  want  to  salt  too  heavily,  for  fear  of  the  enor- 
mous results  exciting  suspicion,  but  despite  his  care  he 
nearly  always  salts  a  little  higher  than  he  intended.  In  a 
mine  where  the  rock  is  hard,  a  miner  may  salt  by  drilling 
holes  and  inserting  mineral  or  ore  and  disguising  the  hole. 
In  loose  ground  or  one  full  of  cracks,  a  shot-gun  loaded 
with  a  moderate  charge  of  gold-dust  will  do  the  work. 
The  skill  of  the  miner  in  this  case  lies  in  his  choice  of  a 
spot  where  he  thinks  it  probable  the  expert  will  take  sam- 
ples, or  in  coaxing  the  expert  to  take  samples  from  such 
ground.  In  hard  ground  the  expert  may  avoid  such  salt- 
ing by  having  the  work  blasted  out  in  his  presence  till  a 
purely  fresh,  virgin  face  is  shown  and  then  taking  his  sam- 
ple. These  precautions  are  not  necessary  under  all  cir- 
cumstances, but  only  in  such  cases  where  the  expert  has  a 
suspicion  that  there  is  an  attempt  to  "  put  up  a  job"  on  him. 
After  getting  his  samples,  and  as  many  as  possible,  he 
will  sack  and  seal  them  then  and  there  in  the  mine,  and 
never  lose  sight  of  them  until  he  has  expressed  them  to  his 


\ 


367 


own  home.  Sometimes  a  mine  is  so  timbered  up.  that 
sampling  is  difficult.  Now  as  they  go  down  the  shaft,  it 
may  be  the  expert  remarks,  "  I  should  like  to  take  a  sample 
in  this  shaft,  but  it  is  so  timbered  up  that  I  don't  see  how 
we  can  do  it  without  ripping  out  some  of  these  boards." 
"  Why  of  course,  so  you  oughter,"  says  the  miner,  "  and 
see  here,  I  think  this  board  is  loose."  Now  beware  lest 
that  board  was  purposely  loosened  and  behind  it  the 
ground  is  salted. 

By  taking  a  great  number  of  samples  at  comparatively 
close  intervals,  provided  afterv,Mrds  the  samples  are  not 
tampered  with,  the  expert  is  less  liable  to  be  deceived  by 
salting,  than  if  he  took  very  few.  A  mine  cannot  be  salted 
all  over  from  end  to  end  if  it  is  a  large  one,  only  at  judi- 
cious intervals,  and  it  will  be  hard  if  the  expert  does  not 
escape  some  of  t'lose  intervals  and  get  some  true  samples. 

Besides  taking  his  regular  assay  samples  by  cutting  all 
around  the  walls,  roof  and  floor  of  the  tunnels  at  intervals 
of  five,  ten,  or  twenty  feet,  according  to  circumstances, 
crushing  and  quartering  the  debris,  and  finally  sacking 
and  sealing  his  sample  bags,  he  should  occasionally  take  a 
"  grab  sample,"  or  a  bit  of  rock  at  random,  or  a  small  sack- 
ful from  the  great  mass  of  his  samples,  and  put  them  in  his 
coat-pocket,  and  keep  them  on  his  person,  to  act  as  a  refer- 
ence in  case  of  any  possible  tampering  or  accident  to  his 
samples  whilst  in  the  vicinity  or  in  transit.  He  should 
also  take  bulk  samples,  good-sized  chunks  of  uncrushed  rock 
which  should  agree  with  the  assay  results  of  his  quartered 
samples. 

A  disadvantage  an  expert  is  under  in  a  strange  camp,  if 
he  cannot  take  his  own  assistant  with  him,  is,  that  he  is 
very  much  at  the  mercy  of  the  miner,  if  any  hard  work  has 
to  be  done,  such  as  blasting  or  hard  digging.  Whilst  en- 
gaged in  such  work  the  miner,  if  he  pleases,  has  many 
chances  of  scattering  around  a  little  gold-dust  on  the  rock 
of  the  vein  or  the  loose  dirt  of  a  placer. 

Whilst  gold-dust  is  the  favorite  medium  for  salting  a 
gold  mine,  chloride  of  gold  is  sometimes  used.  The  lat- 
ter, however,  is  rather  a  dangerous  and  barefaced  trick  to 
try  on  a  competent  expert,  as  its  quality  can  readily  be 
detected  by  the  chemist,  it  being  soluble  in  water.  In  a 
case  of  this  kind  that  came  to  our  knowledge,  an  experi- 


268 

eticed  expert  had  examined  a  certain  mine  and  condemned 
it.  Later,  the  owner  who  was  an  honorable  man.  asked 
him  if.  as  a  special  favor,  he  would  re-examine  it.  as  in  his 
absence  the  assay  values  from  the  mine  had  of  late  shown 
much  better  results.  The  expert  reluctantly  consented  to 
do  this,  though  contrary  to  his  general  rule.  In  going 
along  the  workings  he  noticed  here  and  there  on  the  walls 
certain  patches  and  streaks  of  clay  or  mud,  he  had  not  ob- 
served on  his  first  visit.  Guessing  what  they  were,  he 
casually  observed  to  the  miners,  "  Seems  to  have  been  rain- 
ing in  the  mine  since  I  was  here."  However,  to  the  great 
delight,  doubtless,  of  the  miners  he  took  several  samples 
of  these,  and  forwarded  them  to  a  reliable  chemist.  The 
latter  pronounced  them  chloride  of  gold.  This  of  course 
gave  the  salting  schemie  away,  as  chloride  of  gold  does  not 
occur  free  in  nature,  much  less  in  a  mine.  The  owner  of 
the  mine  was  exceedingly  angry  when  he  learned  what  the 
miners  had  done  without  his  knowledge  or  connivance. 
The  men  themselves  being  commonly  more  or  less  inter- 
ested in  the  sale  of  a  mine,  are  apt  to  try  and  salt  it  with- 
out any  connivance  of  the  owner  or  superintendent.  We 
heard  of  a  case  in  the  San  Juan  district  where  a  mine  that 
was  fairly  good  was  about  to  be  examined.  This  mine 
carried  occasionally  specimens  of  the  very  rich  ore  called 
ruby  silver.  Not  satisfied  with  the  fair,  natural  richness 
of  the  mine,  the  miners  must  needs  import  into  the  hole 
quantities  of  ruby  collected  from  other  mines  in  the  dis- 
trict, whose  men  were  of  course  in  sympathy  with  the 
scheme  and  probable  sale.  This  was  acting  without  the 
knowledge  of  the  owners. 


,    SALTING  GOLD  PLACERS. 

Although  a  gold  placer  usually  covers  a  very  large  area 
of  ground,  it  is  possible  to  salt  it.  Usually  a  miner  shows 
up  his  placer  by  opening  up  pits  at  convenient  intervals, 
so  as  to  cover  the  property.  Nothing  is  easier  than  to  salt 
these  pits  with  gold-dust.  Consequently  whilst  an  expert 
will  examine  these  holes  and  pan  the  dirt,  he  should  be  on 
his  guard,  and  insist,  where  possible,  on  holes  being  freshly 
dug  in  his  presence.  Even  then  he  is  not  safe.  Generally 
in  a  placer,  by  the  cutting  of  a  stream,  sections  are  shown 


269 

sometimes  from  grass  roots  to  bed-rock.  From  such  he 
should  take  and  pan  samples  at  different  levels  in  the  ex- 
posure; this  too,  privately  and  without  too  much  super- 
vision of  the  interested  miner. 


SALTING  ASSAY   SAMPLES. 

This  may  be  done  in  several  ways.  If  the  expert  is  im- 
prudent enough  to  allow  a  miner  to  accompany  and  assist 
him  in  breaking  down  or  crushing  samples  or  panning 
them,  then  the  infusion  of  a  little  gold-dust  is  easy. 
Again,  after  the  expert  has  made  up,  sacked  and  duly 
sealed  his  samples  with  wax,  should  he  leave  them  any- 
where within  reach  of  the  miners,  they  are  not  wholly 
safe,  for  the  miner  may  insert  the  point  of  a  fine  syringe 
containing  gold-dust  into  the  bag,  or  he  may  make  a  bread 
mould  of  the  wax  seal,  open  the  sacks,  and  either  change 
the  ore  for  richer,  or  infuse  some  gold-dust.  Changing  of 
samples  for  others  is  not  an  uncommon  trick.  The  expert 
cannot  watch  his  samples  too  closely.  He  should  sack  and 
seal  them  on  the  ground,  sleep  with  them  under  his  pillow 
if  need  be  at  night,  yet  even  then  cases  have  been  known 
when  the  wary  miner  has  succeeded  in  extracting  and 
changing  them  for  bags  to  all  appearance  exactly  similar. 
The  samples  are  never  safe  till  boxed  up  and  expressed 
and  on  the  way  to  the  city  address.  He  should  never  fail, 
as  we  have  said,  to  have  partial  duplicates  of  these  about 
his  person. 

If  the  expert  wishes  to  assay  the  ore  at  a  friendly  assay 
office  near  the  mine,  whilst  he  is  grinding  down  his  sample 
to  dust,  an  innocent  looking  miner  may  loaf  in,  and  whilst 
watching  the  operation,  accidentally  upset  the  ashes  in  his 
pipe  over  the  sample.  Probably  these  ashes  contain  gold- 
dust,  and  we  might  here  observe  that  a  single  grain  of  gold 
smaller  than  a  pin's  head  may  materially  alter  the  results 
of  an  assay. 

Some  years  ago  an  individual  who  had  succeeded  in 
booming  a  certain  placer  district  and  getting  up  an  excite- 
ment and  a  rush,  constituted  himself  as  a  referee,  and  pro- 
fessor; and  when  miners  brought  samples  for  his  inspec- 
tion, they  were  always  found  to  be  very  rich  in  gold.  But 
similar  samples  from  the  same  spot  if  uninspected  were 


27© 


somehow  invariably  barren.  The  wizard's  mere  look 
seemed  to  change  the  sand  into  gold,  until  it  was  found 
that  he  concealed  in  his  ringer-nails  "  which  were  taper"  not 
wax,  but  fine  particles  of  gold.  Hence.  Midas-like,  what- 
ever he  touched  he  turned  into  gold.  Whilst  the  Salter  may 
lay  traps  for  the  expert,  the  expert  may  sometimes  lay  traps 
for  the  Salter.  An  expert,  who  had  reasons  to  suspect  a 
certain  mine  he  was  examining  had  been  tampered  with, 
and  guessing  there  was  a  likelihood  of  an  attempt  on  his 
samples,  after  securing  himself  with  duplicates,  left  his 
samples  exposed  on  the  floor  of  his  room  at  the  hotel,  then 
went  out  and  hired  a  reliable  Mexican  boy  to  watch  his 
room  and  report  to  him  immediately  if  he  saw  any  one 
enter  it.  He  had  not  long  to  wait.  At  dinner  the  boy 
tapped  him  on  the  shoulder,  and  he  went  to  his  room  and 
caught  the  miner  in  the  act  of  tampering  with  his  samples. 

Sometimes  miners,  if  wealthy  enough,  will  go  to  great 
expense  to  salt  a  property.  Some  miners  took  a  couple  of 
well-to-do  eastern  capitalists  to  a  certain  placer,  panned 
the  gravel  before  their  eyes  and  showed  up  wondrous  col- 
ors. The  investors  having  been  warned  of  miners'  ways, 
refused  to  entirely  swallow  the  bait,  but  told  the  boys  to 
go  ahead  and  develop  the  property,  and  if  at  their  next 
visit,  it  showed  up  as  well  as  the  pans  did  on  this  occasion, 
they  would  buy  it.  When  the  easterners  were  gone,  at  a 
cost  of  several  thousand  dollars  they  built  a  flume,  put  in 
a  hydraulic  plant,  and  gathered  a  pile  of  loose  dirt  to  wash 
down  the  flume,  where  the  gold  is  gathered  upon  quick- 
silver. The  "  sharks"  raised  $50,000  for  a  gold-dust  fund. 
This  dust  was  run  evenly  over  the  quicksilver  so  that,  when 
the  capitalists  returned,  there  was  everything  to  show  an 
enormously  rich  placer-ground.  The  capitalists  insisted 
upon  a  clean-up  after  the  first  fortnight's  run,  which  added 
so  much  more  joy  to  the  sharks.  This  time  the  bait  was 
swallowed  whole,  string  and  all.  The  capitalists  paid 
down  promptly  $250,000  for  the  ground.  The  sharks  left 
the  country.  In  a  few  weeks  nothing  could  be  found  but 
the  amalgam  of  the  sharks. 

An  ingenious  trick  once  baffled  some  experienced  ex- 
perts and  came  very  near  selling  a  mine.  The  mine  was  a 
well-developed  one  and  had  done  great  things  in  its  day. 
It  was  claimed  that  at  the  face  of  the  tunnel,  or  where  the 


271 


workings  left  off,  there  was  still  a  fine  showing  of  ore  in 
place  to  go  on  with.  The  experts  found  it  as  stated ;  on 
the  face  or  end  of  the  tunnel  there  was  a  fine  showing  of 
ore,  and  the  probable  amount  in  place  and  for  the  future 
was  duly  measured  up  and  estimated.  It  leaked  out  later 
that  this  block  of  ore  was  only  a  thin  screen  purposely  left, 
all  back  of.  and  behind  it.  having  been  carefully  worked 
out  and  the  opening  for  the  miners'  ingress  and  egress  skil- 
fully concealed.  The  mine  was  re-examined,  the  cheat 
discovered,  and  the  reputation  of  the  experts  saved  as  well 
as  many  thousands  of  dollars  from  the  pockets  of  guileless 
investors. 

This  brief  sketch  of  some  of  the  ways  of  some  miners,  for 
some  regions  and  properties,  would  give  an  unfair  idea  of 
some  mines  and  miners  as  a  whole,  if  it  were  supposed  that 
all  miners  are  given  to  salting,  and  all  properties  for  sale 
are  beset  by  a  network  of  dishonest  devices.  On  the  con- 
trary, many,  very  many,  miners  are  as  straight  as  a  string 
and  hundreds  of  properties  are  to  be  examined  without  fear 
of  tampering.  But  it  often  happens  that  a  miner,  who  in 
every  other  relation  of  life  is  as  honest  as  the  day.  draws 
a  line,  when  it  comes  to  the  selling  of  a  mine,  which  he 
considers  "  fair  game." 

But,  as  elsewhere  the  world  through,  honesty  pure  and 
simple  is  the  right  policy,  and  in  the  end  would  be  found 
the  best  paying  one.  For  the  notorious  dishonesty  con- 
nected with  mines  (much  more  common  in  the  past  than  in 
the  present)  scares  away  capitalists  from  investing,  whilst 
if  truth  and  honesty  were  maintained,  money  would  roll  in 
freely. 

One  lesson  at  least  may  be  learned  from  what  we  have 
said,  and  that  is,  that  if  in  some  cases  a  professional  expert 
is  ever  taken  in,  what  chances  has  a  capitalist,  ignorant  of 
mines,  to  buy  a  mine  on  his  own  examination?  What  man 
ignorant  of  horseflesh  would  venture  to  buy  a  steed  from  a 
professional  horse-jockey,  without  taking  with  him  a  friend 
who  is  knowing  about  horses? 

How  much  more  so  in  such  a  difficult  and  delicate  prob- 
lem as  that  of  purchasing  a  mine,  is  it  the  duty  of  an  investor 
never  to  purchase  or  induce  his  friends  to  purchase  a  mine, 
until  he  has  employed  the  services  of  a  competent  expert 
to  previously  examine    it.     If    the    expert's    fee   should 


•7« 

amount  to  a  few  hundreds,  and  after  all  he  should  decide 
on  condemning  the  property,  it  is  far  better  for  the  com- 
pany to  entail  this  expense,  and  perhaps  lose  this  small 
sum,  than  to  involve  themselves  in  the  loss  of  thousands 
of  their  own  as  well  as  other  people's  money  in  a  bogus, 
worthless,  or  wildcat  scheme. 


CHAPTER  XXII. 

PROSPECTORS'  TOOLS  AND  HOW  TO  SHARPEN  AND 

TEMPER  THEM. 

The  principal  tools  a  prospector  takes  into  the  field  are 
picks,  drills,  hammers  and  shovel. 

A  prospector,  especially  when  climbing  mountains,  likes 
to  be  as  light-handed  and  unencumbered  as  possible. 

For  his  trip  as  a  whole,  he  may  carry  several  different 
tools  packed  on  his  donkey,  but  when  he  has  arrived  at  a 
locality,  the  vicinity  of  which  looks  likely,  he  leaves  most 
of  his  heavier  tools  in  his  temporary  camp,  or  near  to 
where  he  pickets  his  pack  animal.  He  makes  a  short  ex- 
cursion up  the  mountain  for  a  general  reconnoitre,  armed 
with  nothing  more  than  a  light  prospecting  pick,  weighing 
not  more  than  three  or  four  pounds.  This  little  pick  is 
about  ten  inches  in  length,  with  a  handle  about  fifteen 
inches  long;  the  longer  portion  is  sharpened  into  a  pick, 
and  the  shorter  ends  in  a  square-faced  hammer.  We  recom- 
mend a  square  sharp-cornered  face  to  the  hammer,  in  pref- 
erence to  the  bevelled  face,  as  the  sharp  edges  and  corners 
are  better  adapted  for  breaking  rock  than  the  rounded  or 
bevelled  ends.  This  prospecting  pick  or  geological  pick 
and  hammer,  should  be  all  of  good  steel,  with  a  good  sized 
eye  to  admit  a  springy  handle  of  hickory.  See  Plate 
CXXV,  Figs.  1,  I,  I. 

Armed  with  this  little  weapon  he  climbs  the  hillside, 
hunting  for  "  float"  or  for  rusty  outcrops  of  ledges.  Loose 
pieces  of  rock  he  cracks  open  with  the  hammer  end,  softer 
rock  in  place  he  explores  with  the  pick.  "When  I  am 
climbing  over  the  hills,"  said  an  old  weather-beaten  pro- 
spector to  me.  "  I  want  nothing  but  my  little  pick,  then  if 


«73 


I  find  anything  likely  'in  place.'  I  mark  the  spot,  and  go 

on,  and  at  noon  I  come  down  to  camp,  or  to  where  the 

'burro'  is  feeding,  I  take  up  my  heavy  digging  pick  and 

shovel  and  'open  up';  this  will  occupy  me  till  evening  at 

least,  then  if  I  find  tnere  is  a  ledge 

worth  more  thorough  exploring,  I 

leave  my  tools  by  the  hole,  and 

next  morning  bring  up  the  drills, 

hammers  and  blasting  outfit.   But 

the  first  thing  I  would  advise  a 

tenderfoot,  is  to  get  his  eye  trained, 

trained  to  looking  for  float  and 

observing  mineral  signs,  trained 

to  the  whole  business  of  close 

observation.    Why !  I  myself,  old 

hand  as  I  am,  after  being  away 

for  some  months  about  town  or 

looking  at  other  things,  can't  get 

my  eye  in  and  down  to  it  for  two 

or    three  days;  then  it   kind    of 

comes  natural. 

"You    must  have  an    eye  for 
float  and  rocks  like  an  artist  has 

an  eye  for  color,  and  a  musician  an  ear  for  music.  A 
tenderfoot  had  better  go  along  with  an  old  hand  for  a  few 
days  to  get  into  training." 

DESCRIPTION  OF  TOOLS,  PICKS  AND  DRILLS. 

Picks  and  drills  are  the  main  tools  that  need  sharpening 
and  tempering.  The  kind  of  sharpening  and  nature  or  de- 
gree of  tempering  depend  upon  the  kind  of  work  or  kind 
of  rock  to  be  worked,  whether  hard  or  soft,  loose  grained  or 
flne  grained,  siliceous  or  clayey.  Drills,  for  example, 
would  have  to  be  differently  sharpened  and  tempered  for 
hard  vitreous  quartzite  than  for  soft  sandstone  or  hardened 
clay.  The  same  remark  applies  also  to  picks.  Picks  may 
be  double  pointed  or  single,  or  with  a  hammer  head  called 
a  poll,  if  It  is  to  be  used  for  breaking  rock.  The  main 
points  of  a  pick  are,  strong  cutting  tips,  stout  eye  and  a 
tight  handle.  The  little  prospecting  pick  is  made  of  the 
best  steel  throughout,  but  in  tne  heavier  pick,  the  wearing 


Plate  CXXV. 


3U 

parts  ar«  the  tips,  which  should  be  replaceable.  An  all 
Htee!  pick  is  liable  soon  to  bo  shortened  up  and  useless, 
whilst  the  iron  pick  eye.  a  14  inch  length  of  best  iron, 
gives  long  service  by  welding  on  tip  ends,  whenever  de- 
sired. Professor  Ihlseng,  in  his  "  Manual  of  Mining."  as  also 
Mr.  George  Andre,  in  his  book  on  "  Rock  Blasting,"  gives 
excellent  descriptions  of  tools  used  as  well  as  the  mode  of 
sharpening  and  tempering  them  ;  to  them  we  are  indebted 
for  many  of  the  details  ot  this  article,  and  to  their  works 
we  refer  the  reader  for  fu'  ther  information  on  this  sub- 
ject. "  The  picks  are  sharpened  to  form  on  an  anvil,  and 
commonly  drawn  to  a  four-sided  pyramidal  point,  for  hard 
rock,  and  a  slim  taper  for  fissured  rock,  and  a  bluff  taper 
to  cut  crisp  ground,  and  to  a  chisel ,'  nd  for  chipping  the 
ground.  The  eye  is  oval  and  well  surrounded  with  metal. 
All  the  strain  of  the  prying  falls  on  the  eye.  which  must  be 
true  and  stout." 

DRILLS. 

"  The  dnV  is  a  bar  which  has  one  cutter  edge  and  one 
hammer  end.  It  is  of  round  or  octagonal  steel.  Drills 
may  be  of  various  lengths,  from  a  foot  to  four  or  five  or 
even  more  feet.  For  prospecting  purposes  two  or  three 
medium  short  drills  from  two  to  four  feet  are  generally 
enough,  as  the  prospector's  business  is  rather  to  find  than 
to  develop.  In  beginning  to  drill,  it  is  common  to  use  a 
short  thick  drill,  with  a  stout  'bull  edge'  rather  than  a 
thin,  tapering  one.  especially  in  hard  rock ;  smaller  sized. 
i.e.,  narrower  drills  may  be  used  for  increasing  depth. 

"  The  rock  drill  consists  of  chisel  edge,  bit.  stock  and 
striking  face.  To  allow  the  tool  to  free  itself  readily  in 
the  bore  hole,  and  to  avoid  introducing  unnecessary  weight 
onto  the  stock,  the  bit  is  made  wider  than  the  latter. 
In  hard  rock,  the  liability  of  the  edge  to  fracture  increases 
as  the  difference  of  width;  the  edge  A  the  drill  may  be 
straight  or  slightly  curved,  a  straight  edge  cuts  more  freely 
than  the  curved;  a  bull  bit  for  hard  rock  is  generally 
curved,  a  straight  edge  is  weaker  at  the  comers  than  the 
curved.  The  width  of  bits  varies  from  i  inch  to  2  >i  inches. 
Figs.  I,  2,  la,  2d,  Plate  CXXVI,  show  the  straight  and 
curved  bits  and  angles  of  cutting  edges  for  use  in  rock. 
The  stock  is  octagonal  in  section.     It  is  made  in  lengths 


//". 


...i' 


»75 


varying  from  20  inchvs  to  42  inches.  The  shorter  the  stoik, 
the  more  effectively  it  transmits  the  forte  of  the  blow.  To 
insure  the  longer  drills  working  freely  in  the  hole,  the 
width  of  the  bit  should  be  very  slightly  reduced  in  cat  I. 
length.  Diameter  of  stock  is  less  than  the  width  of  the  bit 
generally  by  ^  of  an  inch. 

"The  smith  cuts  up  the  'borer'  steel  bars  into  desired 
lengths  to  form  the  bit,  the  end  of  the  bar  is  heated  and 
flattened  out  by  hammering  to  a  width  a  little  greater  tlian 
the  diameter  of  the  hole  to  be  bored.    The  cutting  edge 


n 


Fl9,4. 


& 


DrUt  tn 
in  roe*. 


^—fM,  MMta, 


ab  3r 

Plate  CXXVI. 

Forms  of  Drills. 

is  then  hammered  up  with  a  light  hammer  to  the  requisite 
angle  and  corners  beaten  in  to  give  the  exact  diameter  of 
the  bore  hole  intended.  The  drills  arc  made  in  sets  and  the 
the  longer  stocks  will  have  a  bit  slightly  narrower  than  the 
shorter  ones  for  reasons  already  given.  The  edge  is  touched 
up  with  a  file.  Heavy  hammering  and  high  heats  should 
be  avoided.  The  steel  should  be  well  covered  with  coal,  in 
making  the  heat,  and  protected  from  the  raw  air.  Over- 
heated or  burned  steel  is  liable  to  fly,  and  drills  so  injured 
are  useless  until  the  burned  portion  has  been  cut  away. 
Care  is  required  to  form  the  cutting  edge  evenly,  and  of 
the  full  form.  If  the  comers  get  hammered  as  in  Fig.  3a, 
Plate  CXXVI,  they  are  said  to  be  'nipped'  and  the  tool 
will  not  free  itself  in  cutting.     When  a  depression  of  the 


27^ 

straight  or  curved  line  forming  the  edge  occurs,  as  Fig.  ib, 
"  the  bit  is  said  to  be  'backward'  and  when  one  of  the  cor- 
ners is  too  far  back,  as  Fig.  y,  it  is  spoken  of  as  'odd  cor- 
nered.' Either  of  these  defects  causes  the  force  of  the 
blow  to  be  thown  upon  a  portion  only  of  the  edge,  which 
is  thereby  overstrained  and  liable  to  fracture." 

SHARPENING  TOOLS.  , 

Professor  Ihlseng  in  his  "  Manual  of  Mining"  says :  "  The 
best  fuel  for  blacksmithing  may  be  a  slightly  caking  coal, 
giving  flame  and  high  heat.  Coke  is  hotter  but  harder  to 
keep  fire  in.  The  fuel  should  be  as  free  from  sulphur  as 
possible.  White  ash  coal  is  better  than  red  ash ;  sulphur 
makes  the  iron  hot  short,  and  tends  to  produce  scales.  The 
coal  should  be  clear  of  shale  or  slate,  for  they  fuse  and 
make  a  pasty  cinder  that  is  annoying." 

A  prospector  away  from  civilization  may  have  to  use 
wood;  in  that  case  he  should  use  chips,  and  blow  them 
with  a  portable  bellows. 

The  prospectors  who  try  to  get  along  on  as  small  an  out- 
fit as  possible  usually  take  one  to  three  blasting  powder 
cans  and  cut  the  heads  out  of  all  but  the  bottom  one,  and 
one  head  of  that  must  be  cut  out ;  these  they  place  one  on 
top  of  the  other  to  make  a  furnace.  They  punch  an  inch 
and  a  half  hole  in  the  side  of  the  bottom  one  at  the  bottom 
tor  draft,  and  to  put  in  the  points  of  the  tools  to  heat  them. 

They  use  charcoal  for  fuel  and  then  a  chunk  of  steel  or 
railroad  iron  about  6  inches  long  serves  fo;  an  anvil. 
Some  take  a  small  bellows  and  anvil  with  them.  For  tem- 
pering drills  they  give  the  drill,  when  red,  a  plunge  in 
water.  After  two  or  three  rubs  on  wood,  to  brighten  it, 
they  hold  it  up  to  the  light  and  watch  it  until  it  takes  on  a 
straw  color.  Then  they  dip  it  in  water  again.  For  picks 
a  blue  color  is  the  most  satisfactory  in  general. 

"  Steel  is  a  compound  of  iron  and  carbon,  and  its  homo- 
geneity and  presence  of  carbon  impart  to  it  a  capability 
of  hardening  and  tempering  to  a  degree  depending  on  the 
temperature  of  the  heating  and  subsequent  cooling.  As 
the  amount  of  carbon  increases,  the  melting  point  of  the 
iron  decreases,  and  this  greater  fusibility  reduces  its  weld- 
ing quality. 


■  f 


277 

"  A  steel  is  called  'hardened'  when  it  has  been  suddenly 
cooled  and  thereby  become  as  hard  as  possible.  This  is 
owing  to  the  presence  of  carbon,  for  pure  malleable  iron 
is  not  affected  by  the  operation,  while  both  steel  and  cast 
iron  are  to  a  marked  degree. 

"  The  operation  consists  in  forging  the  steel  to  a  certain 
degree  of  temperature,  and  then  plunging  it  into  some 
fluid  which  abstracts  the  heat  from  the  tool.  The  quicker 
it  is  done,  and  the  greater  the  difference  of  temperature, 
the  harder  is  the  tool.  Either  water  or  oil  is  used ;  both 
volatilize  at  a  temperature  much  below  that  of  the  im- 
mersed tools,  so  the  hardening  takes  place  in  a  vapor ;  oil 
generally  produces  the  best  effects.  On  the  first  plunge 
the  metal  is  chilled  and  coated  with  soot,  after  which  a 
slow  process  of  cooling  takes  place." 


t  TEMPERING. 

"  Tempering  follows  hardening,  whereby  the  steel  is  sub- 
jected to  a  subsequent  lower  heat,  which  softens  it,  and  re- 
moves its  brittl3ness.  When  the  hardened  iron  is  slowly 
reheated,  its  surface  gradually  assumes  phases  of  color, 
beginning  with  a  light  straw,  passing  through  shades  of 
yellow,  brown,  purple,  blue  and  red.  At  a  cherry-red 
heat,  the  original  color  before  hardening,  the  effects  of  the 
chilling  are  practically  removed. 

"  Tempering  consists  in  carrying  the  second  heat  to  one 
of  the  above  mentioned  colors,  according  to  the  amount  of 
the  brittleness  to  be  annealed.  This  depends  upon  the  use 
to  which  the  article  is  to  be  put.  A  second  stage  of  the 
operation  finishes  the  job.  The  aforementioned  reheat 
goes  on  a  little  way  beyond  the  desired  color.  The  tool  is 
carefully  plunged  part  way  into  the  water  or  oil,  till  the 
disappearance  of  the  steam  indicates  that  it  is  cold,  when 
another  portion  of  the  distance  is  further  immersed  for  a 
moment.  The  tool  is  withdrawn,  the  scales  rubbed  off  and 
the  heat  of  the  remaining  portion  draws  to  the  edge,  until 
it  has  assumed  the  proper  tempering  color.  It  is  then  thor- 
oughly cooled.  The  idea  that  the  steel  is  cool  :;r  at  a  blue, 
than  at  a  yellow,  in  final  drawing,  is  erroneous;  for  more 
of  the  heat  is  conducted  from  the  red  portion  to  the  point, 
than  it  radiates  to  the  air,  and  the  first  heat  to  the  edge 


278 


only  gives  a  yellow ;  with  more,  it  becomes  purple,  and  so 
on.  Hardened  drill  and  pick  points  are  treated  in  this  way, 
4"  of  the  end  being  heated  to  a  yellow ;  and,  in  thirds,  the 
tempering  is  proceeded  with  as  above. 

"  Care  should  be  taken  that  the  plunged  tool,  while  tem- 
pering, be  not  held  too  long  a  time  at  a  certain  color  line, 
as  it  has  a  tendency  to  break  at  that  point.  The  tool 
should  be  slightly  waved  in  the  water.  '  Pieces'  which  are 
to  be  tempered  throughout  must  be  allowed  to  soak,  i.e., 
become  uniformly  hot,  before  plunging. 

"The  proper  color  for  a  given  ground  is  only  ascer- 
tained by  experience.  Generally  speaking,  the  picks  and 
drills  are  stopped  at  a  '  straw, '  if  intended  for  hard  ground ; 
at  a  blue,  for  mild  ground.  The  toughness  of  the  steel 
should  be  preserved  as  much  as  possible,  therefore  select 
the  lowest  color  compatible  with  the  service  to  be  per- 
formed. A  high  carbon  steel  is  given  a  lighter  color  than 
steel  of  low  carbon. 

"  A  pick  is  made  of  a  square  iron  bar  14"  x  i%"  heated 
at  the  middle,  and  then  struck  endwise,  till  r.bout  ij4" 
across.  This  spot  is  softened,  and  at  red  heat  cut  open, 
and  swelled  by  a  drift  to  form  the  eye.  This  is  then  slit  at 
the  ends,  and  softened,  while  a  6"  length  of  pick  steel  is 
being  heated.  When  ready,  this  steel  is  tong^ied  into  the 
iron,  and  hammered.  A  reheating  with  borax,  and  a  ham- 
mering complete  the  weld,  after  which  the  picks  are  sharp- 
ened and  tempered ;  no  signs  of  the  weld  should  be  visible." 

"  Pick-steel"  is  a  special  steel  that  can  be  had  in  bars 
i%"  or  lyi" X.  }i"  OT  ^•",  and  used  only  for  tips. 

Steel  bars  for  drills  come  in  lengths  of  about  14  feet  ieach 
and  from  }i"  to  2"  diameier.  The  American  "Black  Dia- 
mond" brand  is  a  favorite.  The  bars  are  cut  into  pieces 
as  long  u3  can  conveniently  be  used,  e.g. ,  30"  and  36".  The 
bits  are  wider  than  the  tool,  to  prevent  it  sticking  to  the 
hole.  They  are  widened  according  to  pattern,  so  they  can 
"follow"  well.  The  first  drill  has  the  widest  bit;  the  fol- 
lowers narrower  ones.  In  hard  rock  the  flare  is  smaller 
than  that  in  soft  rock. 

"  The  temper  is  a  lighter  color  for  hard  than  for  soft 
rock.  If  the  edges  of  the  returned  drills  are  cracked  or 
broken  the  steel  is  too  brittle,  and  should  be  made  softer 
or  other  coal  used.     If  the  edges  blunt  much  by  wearing 


'  279 

round  they  are  all  right,  though  a  harder  temperature  may 
give  them  longer  life.  Cast  steel  borers  are  never  heated 
above  a  cherry.     They  are  annealed  at  the  striking  end." 


PRACTICAL   SUGGESTIONS   AND   POINTS   BY   A   BLACKSMITH. 

A  prospector  must  have  something  to  act  as  an  anvil ;  a 
hard  pebble  won't  do,  he  can  carry  a  small  anvil  or  a 
chunk  of  railroad  iron.  A  small  hand  bellows  or  even  a 
portable  forge  worked  with  a  crank  will  make  his  outfit 
complete.  The  following  practical  hints  I  picked  up  from 
a  blacksmith  whilst  watching  him  at  work  tempering  both 
picks  and  drills  for  some  prospectors  He  said :  "  You  must 
temper  your  drill  according  to  the  character  of  the  rocks. 

"  For  hard  rock,  use  a  short  thick  edged  'bull  bit'  which 
will  stand  a  high  brittle  temper  such  as  'straw. '  For  picks, 
a  light  blue  color  is  a  good  temper,  rather  than  'straw' 
which  is  too  brittle.  Cherry  red  is  the  heat  of  your  bar, 
not  hotter;  1  lying  this  on  the  anvil  and  hammering  it  well 
all  over  giv  it  toughness.  If  blisters  show  on  the  steel 
you  must  hammer  it  over  again.  By  occasionally  dipping 
your  hammer  in  water  and  then  striking  with  it,  you  get 
the  steel  down  v  a  fine  grain.  When  you  are  dipping  for 
tempering,  put  the  point  in  the  water,  that  cools  the  point, 
and  the  heat  runs  the  color  down  to  the  cool  point ;  when 
the  color  reaches  the  tint  you  want,  then  is  your  time  to 
cool  oflf  quickly.  The  color  progresses  from  a  white  or 
pale  straw  to  copper  color  to  blue.  Copper  tint  is  a  good 
one  to  stop  at  for  a  drill, — blue,  for  a  pick.  The  right  mo- 
ment to  stop  and  cool  is  just  at  the  turning  point  from  one 
color  to  another." 

He  took  a  piece  of  steel,  heated  it  to  cherry  red,  laid  it 
on  the  anvil  and  pounded  it  lightly  with  his  hammer  all 
over,  to  toughen  it  by  blows,  occasionally  dipping  his  ham- 
mer in  the  water  to  "  water  temper"  it ;  this  further  tough- 
ens it,  by  partially  cooling  it.  Now  the  bar  was  again  put 
in  the  fire  and  heated  to  a  cherry  red,  care  being  taken  not 
to  keep  the  bar  loo  long  in  the  fire,  as  that  would  tend  to 
take  its  toughness  out,  or  produce  blisters.  The  bar  was 
plunged  about  an  inch  into  the  water,  and  then  rubbed 
against  a  brick,  to  show  the  colors  plainer.  These  passed 
from  the  point  upwards,  gradually  through  the  colors  we 


28o 

have  mentioned,  to  arrest  it  by  suddenly  cooling  off  at 
"straw,"  would  make  it  too  brittle  for  ordinary  drills,  ex- 
cept a  "  bull  drill."  Now  the  "  straw"  turns  into  a  copper 
hue,  a  good  point  to  cool  off  for  a  drill.  Now  it  passes 
into  a  blue,  at  this  point  it  would  be  well  to  cool  off  for 
Bipick.  The  edge  of  n  drill  is  almost  of  secondary  impor- 
tance to  the  sharpness  of  the  projecting  corners;  when  these 
are  gone,  the  drill  is  used  up,  and  clogs  in  the  hole. 
Some  rocks  like  sandstone  will,  by  reason  of  the  quartz  in 
them,  wear  off  the  comers  very  rapidly,  others,  like  lime- 
stone or  granite,  less  rapidly. 

Another  blacksmith  advised  me  not  to  dip  (as  is  com- 
monly done)  the  point  only  an  inch  in  water  as  it  is  apt  in 
use  to  break  at  the  water  line,  but  plunge  it  all  over  in  the 
water.     "  Who  shall  decide  when  doctors  disagree?" 

A  prospector  should  take  with  him  a  regular  black- 
smith's hammer  for  sharpening,  as  well  as  the  4  or  5-lb. 
hammer  he  uses  for  striking  drill  or  the  rock. 


CHAPTER   XXIII. 


SOME  ELEMENTS    OP    MINING    LAW    RELATING  TO 

PROSPECTING. 


A  prospector  would  do  well  to  acquaint  himself  with  a 
few  elements  of  mining  law,  so  we  will  give  a  few  samples 
of  Colorado  mining  law  for  his  benefit. 

Extent  of  Lode  or  Claim. — The  length  of  any  lode  may 
equal,  but  not  exceed,  1,500  feet  along  the  vein. 

Dimensions. — The  width  of  lode  claims  in  Gilpin,  Clear 
Creek,  Boulder  and  Summit  counties,  shall  be  75  feet  on 
each  s'de  of  the  center  of  the  vein  or  crevice. 

Certificate  of  Location. — The  discoverer  of  a  lode  shall, 
within  three  months  from  the  date  of  discovery,  record  his 
claim  in  the  oflfice  of  the  recorder  of  the  county  in  which 
such  lode  is  >situated,  by  a  location  certificate,  which  shall 
contain : 


38l 

!st.  The  name  of  the  lode. 
2d.  The  name  of  the  locator. 
3d.  The  date  of  the  location. 

4th.  The  number  of  feet  in  length  claimed  on  each  side 
of  the  center  of  the  discovery  shaft. 
5th.  The  general  course  of  the  lode  as  near  as  may  be. 

Discovery  Shaft.— ^eiore  filing  such  location  certificate, 
the  discoverer  shall  locate  his  claim  by  first  sinking  a  dis- 
covery shaft  on  the  lode,  to  the  depth  of  at  least  10  feet,  or 
deeper  if  necessary,  to  show  a  well-defined  crevice. 

Second,  by  postmg  at  the  point  of  discovery  on  the  sur- 
face a  plain  sign  or  notice  containing  the  name  of  the 
lode,  the  name  of  the  locator  and  the  date  of  the  discovery. 

Third,  by  marking  the  surface  boundary  line  of  the 
claim. 

Staking. —SviCh  surface  boundaries  shall  be  marked  by 
six  substantial  posts,  hewed  or  marked  on  the  side  or  sides 
of  which  are  in  toward  the  claim,  and  sunk  in  the  ground, 
to  wit,  one  at  each  comer,  and  one  at  the  center  of  each 
side  line.  Where  it  is  impossible  on  account  of  bed-rock, 
or  precipitous  ground,  to  sink  such  posts,  they  may  be 
placed  in  a  pile  of  stones. 

Open  Cuts.— Any  open  cut  or  cross-cut  tunnel,  or  tunnel 
which  shall  cut  a  lode  at  the  depth  of  ten  feet  below  the 
surface,  shall  hold  it,  the  same  as  if  a  discovery  shaft  were 
sunk  thereon,  or  an  adit  of  at  least  ten  feet  along  the  lode 
from  the  point  where  the  lode  may  be  in  any  manner  dis- 
•covered,  shall  be  equivalent  to  a  discovery  shaft. 

Time.—T\iQ  discoverer  shall  have  60  days  from  the  time 
of  uncovering  or  disclosing  a  lode,  to  sink  a  discovery 
shaft  thereon. 

Construction  of  Certificate. — The  location  certificate  of  any 
lode  claim  shall  be  constructed  to  include  all  surface 
ground  within  the  surface  lines  thereof,  and  all  lodes  and 
ledges  throughout  their  entire  depth,  the  top  or  "  apex"  of 
which  lies  inside  of  such  lines  extending  downward  verti- 
cally, with  such  parts  of  all  lodes  or  ledges  as  continue  to 
dip  beyond  the  side-lines  of  the  plane,  but  shall  not  in- 


283 

elude  any  portion  of  such  lodes  or  ledges  beyond  the  end 
lines  of  the  claim,  or  at  the  end-lines  continued,  whether 
by  dip  or  otherwise,  or  beyond  the  side-lines  in  any  other 
manner  than  by  the  dip  of  the  lode. 

Cannot  be  Followed. — If  the  top  or  "  apex"  of  a  lode  in  its 
longitudinal  course  extends  beyond  the  exterior  lines  of 
the  claim  at  any  point  on  the  surface,  or  as  extended  verti- 
cally downward,  such  lode  may  not  be  followed  in  its  long- 
tudinal  course  beyond  the  point  where  it  is  intersected  by 
the  exterior  lines. 

Proof  of  Dtvclopment. — The  amount  of  work  done,  or  im- 
provements made  during  each  year  shall  be  that  pre- 
scribed by  laws  of  the  United  States. 

Placer  Mining  Claims.  —  The  discoverer  of  a  placer 
claim  shall,  within  30  days  from  the  date  of  discovery, 
record  his  claim  in  the  office  of  the  recorder  of  the  county 
in  which  said  claim  is  situated,  by  a  location  certificate, 
which  shall  contain : 

I  St.  The  name  of  the  claim,  designating  it  as  a  placer 
claim. 

2d.  The  name  of  the  locator. 

3d.  The  date  of  the  location. 

4th.  The  number  of  feet  or  acres  claimed. 

5th.  The  description  of  the  claim  by  such  reference  to 
natural  objects  or  permanent  monuments  as  shall  identify 
the  claim. 


Before  filing    such  location 
shall  locate  his  claim : 


certificate,   the  discoverer 


1st.  By  posting  upon  such  claim  a  plain  sign  or  notice 
containing  the  name  of  the  claim  and  of  the  locator,  the 
date  of  discovery,  and  number  of  acres  or  feet  claimed. 

2d.  By  marking  the  surface  boundaries  with  substantial 
posts  sunk  in  the  gn*ound,  one  at  each  angle  of  the  claim. 

On  each  placer  claim  of  160  acres,  not  less  than  100  dol- 
lars* worth  of  labor  shall  be  done  by  the  first  of  August 
each  year,  and  upon  less  or  more  ground  a  sum  in  pro- 
portion. 


f' 


INDEX. 


< 


V 


PACK 

Alaska 199.  204 

Andesite    f)i 

Archaean 21,  27,  42 

Argentite <>7 

Arizona 240 

Aspen 68,177 

Augite 54 

Barite 55 

Basalt   25.  61,  62 

Beach  Mining   121.  226 

Beach  Sands 207 

Beds    88 

Bismuthinite 66 

Black  Hills 237 

Black  Sdnd 112 

Blanket  Veins 79.  80,  162 

Blossom 94 

Blue  Limestone 23 

Boise  Basin 231 

Boulder  Mines 126 

Breccia 62 

Brecciated  Veins  82 

British  America 213 

British  Columbia   200,  214 

Brittle  Silver 68 

Calcite 55 

California 223 

California  Placers 224 

Cambrian 22.  30,  42 

Canyons 38 

Carbonates    69 

Carboniferous 23,  33,  45 

Caribou 203 

Caves 174 

Cerussite   70 

Change  with  Depth   104 

Chemistry  of  Rocks 143 

Chlorite 55 


I 


284 


PAGE 

Coal  24 

Colorado  Placers 123 

Contact  Deposits 76 

Contacts 79,  loi,  162 

Copper   70 

Country  Rock 104 

Cretaceous 24.  35,  47 

Cripple  Creek 137,  151,  245 

Cross-cuts 109 

Cross-vein 84 

Dakota 233 

Deep  Leads  i  ig  226 

Devonian   3ii  44 

Diamond  Drill  81 

Diorite 5g.  219 

Dolomite  55 

Dolomitization 182 

Dredging 253 

Dykes loi 

Earth's  Origin 26 

Education  of  Prospector 8 

Effusive  Rocks 61 

Epidote    s 55 

Eruptive  Forces 99 

Examining  Mines  187 

Faults 74.  84,  86 

Feldspar 54 

Fissures 140 

Fissure  Veins 82,  89,  93,  96,  103,  125,  132.  258 

Fluor-spar 55.  63 

Folds 86 

Folding  and  Faulting 77 

Fossils 39,  41,  42 

Eraser 203 

Free-milling 78 

Garnet 55 

Generalized  Section  of  Rocky  Mountains 21 

Geological  Section  of  the  Earth's  Crust 17 

Geological  Training 15 

Glacial  Epoch 37 

Gneiss 5^ 

Gold  in  Archaean  Rocks 29 

Gold  in  Slates 221 

Granite 55 

Gray  Copper 65 

Gypsum 55 


A' 


285 


;i 


. 


PAGE 

Historical  Geology 3 j 

Hornblende   54 

Horn  Silver ....'..'.'.. 68 

'•  Horses" 83 

Hot  Sprines !.....  147 

Hydraulicking !  lai 

Idaho 200 

Idaho  Mines 230 

Igneous  Rocks 58^  103.  132 

Impregnations 88.  92 

Intrusive  Rocks 5g 

Iron !...........  .64 

o'nts. 75,  87 

urassic 24,  47 

ura-Trias 34.  46 

Caolin 173 

Cootenai 202,  216 

-.ake  Ontario  Veins 222 

Laws ! . .  280 

Lavas 1^3 

Leadville • 70/ 167 

Lithology 50 

Loaniing 116 

Locating  Vein 15 

Lower  Canada 219 

Manganese ] 64 

Marble 57 

Mercur  District 255 

Metals.  Table  of 41 

Metamorphic  Rocks 55 

Metasomatic 80 

Mica 54 

Microscopy  of  Rocks 142,  144 

Mineralogy   63 

Minerals 65 

Earthy 63 

Metalliferous 64 

Rock-making ,       e-i 

Table  of Ji 

Mining  Laws   280 

Mining  Terms 90 

Montana 232 

Moraines 38 

Newfoundland 222 

New  Mexico 247 

Northwest,  The 198 


286 


PAuB 

Nova  Scotia aaa 

Obsidian   6a,  107 

Ore-t)earing  Rocks 107 

Oregon aoo 

Ores 65 

Ores,  Free-milling 78 

Ore  Deposits 72,  88,  135,  16a 

Ortiz  \iountains 349 

Outcrop   94 

Outfit 9 

Paleontology 39 

Paleozoic.  Meaning  of 34 

Panning  Gold la,  14 

Pegmatite   57 

Phonolite 15a 

Placers   n.  iii.  133,  347,  253 

Pockets  . . . .  ^ 80,  97 

Polybasite  68 

Porphyries' 31,  58 

Pre-Cambrian 39 

Prospecting,  Sketch  of 11 

Pyrites  66 

luartz 53 

)uartz- Porphyry 59 

martzites 30,  57 

quaternary    25,  49 

Led  Cliff  Gold  Deposits 175 

Reporting  on  Mines 187 

Rhyolite 61 

Richness  with  Depth 98 

Rocks   50.  55,  61 

Igneous    58 

TaV)le  of 41 

Rosita  Mine 136 

Ruby  Silver 65,69 

Salting  Mines 264 

Sampling  Mines  187,  192 

San  Juan  Mines 132 

Schist   57 

Scoria 62 

Sedimentary  Rocks 162 

Serpentine 38 

Sharpening  Tools 272 

Sheared  Dykes 244 

Signs 81,  93 

Silica 147 


«tr 


l>A(->l. 

Silurian 33.  30.  43 

Silver  Bow   Basin  306 

Silver  Reef  88 

Slate   57 

Slickensides 91 

Solfataric  Action 149 

South  Park  Mines 163 

Splits go 

Sulphurets 67 

Steamboat  Springs 150 

S'ephanite 68 

Strike  and  Dip  of  Veins 109 

Syenite 56 

Talc 54 

Tellurium 67 

Tempering  Tools 377 

Tertiary 34.  36.  49 

Tin  Deposits 237 

Tools II 

Tourmaline 55 

Trachyte 62 

Treadwell  Mine 208 

Triassic 24,  47 

Tufa  or  Tuff 62.  141.  146.  15a 

Unconformity 3* 

Values  of  Ores 66 

Veins 14.  82.  89,  95 

Veins  and  Eruptive  Forces 99 

Volcanoes '37 

Walls 9a 

White  Porphyry 60 

Zinc  Blende 7i 


